Your recipe sounds delish indeed. I love mushrooms in everything- however- as you probably know they are not a classic ingredient in linguini with clam sauce. Just in case you are interested I've pasted Marcella Hazan's recipe from her Essentials of Classic Italian Cooking. Buon appetito!

White Clam Sauce

Essentials of
Classic Italian Cooking
by Marcella Hazan, 1993, Alfred A. Knopf

“Everywhere in Venice – or in Italy for that matter – one can eat spaghetti
with clams, but none tastes like the dish Cesare Benelli makes at Al Covo,
the restaurant he owns with his Texan wife, Diane. Cesare’s genial variation
on this timeless theme consists of holding back the natural juices of the just-
opened clams, draining the pasta while it is still underdone, then finishing
the cooking of it in a skillet together with the clam juice. The pasta, by the
time it becomes fully cooked, drinks up all the fresh clam juices, achieving a
density and richness of flavor no other version of the dish can match.”

For 4 servings

1 1/2 dozen littleneck clams
5 tablespoons extra virgin olive oil
2 large garlic cloves, peeled and
sliced paper thin
1 1/2 tablespoons chopped parsley
Chopped fresh hot chili pepper,
2 teaspoons, or to taste
1 fresh, ripe, firm plum tomato, cut into
1/2-inch dice with its skin on, but drained
of juice and all seeds removed
1/2 cup dry white wine
1 pound dry pasta
6 fresh basil leaves, torn into
2 or 3 pieces

Recommended pasta: Spaghettini, thin spaghetti, takes to
clam sauces more successfully than other shapes. A close
enough second is spaghetti.

1. Soak the clams for 5 minutes in a basin or sink filled with cold water. Drain and refill the basin with fresh cold water, leaving in the clams. Vigorously scrub the clams one by one with a very stiff brush. Drain,
   refill the basin, and repeat the whole scrubbing operation. Do this 2
   or 3 more times, always in fresh changes of water, until you see no
   more sand settling to the bottom of the basin. Discard any that, when handled, don’t clamp shut. Put them in a pan broad enough so that
   the clams don’t need to be piled up more than 3 deep, cover the pan,
   and turn on the heat to high. Check the clams frequently, turning
   them over, and remove them from the pan as they open their shells.
2. When all the clams have opened up, take them out of the pan, using a slotted spoon. Try not to stir up the juices in the pan any more than
   you must. Detach the clam meat from its shell, and gently swish each
   clam in the pan juices to rinse off any sand. Unless they are exception-
   ally small, cut them up in 2 or even 3 pieces. Put them in a small bowl,
   pour 2 tablespoons olive oil over them, cover the bowl tightly with
   plastic wrap, and set it aside for later. Do not refrigerate.
3. Line a strainer with paper towels, and filter the clam juices in the pan through the paper and into another bowl. Set aside for later.
4. Choose a skillet or sauté pan broad enough to contain the pasta later.
   Put in 3 tablespoons olive oil and the slice garlic, and turn on the
   heat to medium high. Cook the garlic, stirring it, for just a few
   seconds, without letting it become colored, then add the parsley
   and the chili pepper. Stir once or twice, and add the diced tomato.
   Cook the tomato for 1 to 2 minutes, stirring it from time to time,
   then add the wine. Simmer the wine for about 20 to 30 seconds,
   letting it reduce, then turn off the heat.
5. Cook the pasta in abundant boiling salted water until it is very firm
   to the bite, barely short of being fully cooked. When you bite a
   piece off, it should feel slightly stiff and the narrowest of chalk-
   white cores should be showing in the center of the strand.
6. Turn the heat on to high under the skillet or sauté pan, drain the
   pasta and transfer it immediately to the pan. Add all the filtered
   clam juice, and cook, tossing and turning the pasta, until all the
   juice has evaporated. If the pasta was not too underdone when
   you drained it, it should now be perfectly cooked. Taste it and,
   in the unlikely event it needs more cooking after the clam juices
   have evaporated and been absorbed, add a small amount of water.
7. As soon as the pasta is done, before you turn the heat off, add the
   cut-up clams with all the oil in the bowl and the torn basil leaves,
   toss in the pan 2 or 3 times, then transfer to a warm platter and
   serve at once.

I've previously used tumeric to give a yellow color to sauces. The flavor change is modest and not unwelcome. Any other "food coloring" ingredients I could have used?

I make Schulman's Pureed Mushroom Soup that has a color issue as well as being a bit thick. Too close to the consistency of apple sauce so i thin it quite a bit. With stock and have tried red Miso, (misoMaster). And a pinch of turmeric. Parsley and cilantro stems add a bright flavor as well as color. (leaves for garnish and leeks).

Raw Umber is a tough muddy color to change. I would probably go for thinning a bit as well as a color with a flavor boost. I thought of using beet but that would just be a pinkish brown. Thinning would be my choice so your sauce is not so clingy and your veg retains its colors.

My Vongole does not have much color at all and is very thin. Lots of garlic, parsley and leek. Very al dente pasta is finished its cooking in the clams juice. Garnish for color. Half the little necks i serve in the shell and on each plate.

That does sound good and I hope you find a cure for your grey!

I'm just glad you puree it. I can't stand sliced mushrooms with clams/oysters. The texture is too similar :) Maybe itty bitty bits would also work, but not the same size. It's like playing, wonder which thing this bite will be?

Something dark, like kale, might do it, but if the rules of paint hold, it's the cream that made the mushrooms gray. Maybe try butter and stock instead? If you cook them down with a little dark wine or stock (rather than clear) so they shed all their water, and steam them off, that will get them browner. In my experience, most people don't give the mushrooms the time they really
need to shrink down and get their full flavor and color. After
sautéing them, cover for 8-10 minutes on med-low, then stir until the
pan is pretty dry. It also helps if you use a darker mushroom, like cremini (I don't know if that's what you used), but since you were using stems, I'm guessing they were left from using the caps for something else, so maybe there wasn't a choice. Anyway, once you've gotten the mushrooms as brown as possible, you might get a better color out of a purée.