Looks pretty good! Keep it up!

https://www.deckbuilderspringfieldma.com

Stark white ceiling and Sunshine Day Yellow for the screened porch wall -- which shouldn't look out of place with the sage exterior wall.

http://www.materials-world.com/paint-colors/valspar_lows_laura_ashley/valspar_lowes_tradition/valspar_lowes_tradition_01.htm

In the south a lot of porch ceilings are painted sky blue because that seems to discourage insects from making nests against the ceiling -- supposedly they think the ceiling is sky.

You could paint the ceiling and the wall blue but before you do decide to use blue for your porch, paint something else the blue you are considering and stand it against the exterior wall and see if you think you will like the contrast.

MGal, I'm curious, what did you end up painting your porch?

In case your project hasn't been done, yet, I have a very different opinion from those earlier suggestions. Looking at your contemporary kitchen with the warm gray tones and warmer white cabinetry, I (personally) do not see light (haint) blue as an option for the ceiling. I love that look for a traditional home or a Southern-style home, but it seems very "off" and out-of-place for the adjacent look of your contemporary kitchen. Your angled siding and deck pattern are also more contemporary than traditional. As for the idea of painting the walls "Sunshine Day Yellow"--yellow has its place, but not with ANY of your colors currently inside or outside of your home!

If that were my porch, I'd continue with the contemporary theme and undertones of the kitchen walls. (Are your kitchen walls perhaps Benjamin Moore Revere Pewter or some similar color?) The ceiling could be the same as your white cabinetry. If you want the entire porch lighter, then paint it in a lighter version of the kitchen or the matching white of your kitchen trim. That would provide better flow and be easier on the eye, especially with all the natural green beyond the porch. Your rug, furniture, pillows, etc. could repeat the kitchen colors which are very neutral. Adding paint colors such as light blue, bright yellow (!), and the somber green-gray of your home's exterior are too different from one another.

Your porch decking is a gray with either a blue or purple undertone (on my screen); your home's exterior and the porch wall is a gray with a green undertone (or perhaps a "sagey" color). Your kitchen has a warm gray tone. Those tones aren't working together. Let the kitchen inspire the rest attached to it. The porch floor looks like it is ready to be freshened up so maybe the house needs painting, too? Consider changing the gray-green exterior, too, and that should help connect it all to your kitchen--which is BEAUTIFUL, by the way! Hope it all turned out/turns out great!

You win the prize! What you have outlined is EXACTLY what we have done — including for the exterior siding, which we painted a color called fawn brindle with French grey trim. We may the screem porch a beautiful light cream color and it really looks like an extension of the kitchen. We added a tongue in groove paneling to the ceiling and also added recessed lights. For furniture www went with a huge outdoor sectional which I thought might be crammed ans we would have to remove some pieces. But it is so in proportion that the room actually feels much bigger than. We have so enjoyed this room with the make over! We are away at the moment but when I return I’ll post some pics!

Porch ceiling = haint blue. At least in my mind. Lots of flexibility in a haint blue, so I’d go with a light grey blue.