ooopps,...

Ideas are fine but they don't always help unless the plan is to gut the space. Painting is the right idea, I think but, of course, the wallpaper needs to be removed first. Then there are 3 decisions to make: 1- Will the counters be left or replaced. 2- Will the cabinets be painted as well as the walls. 3- Is there room in the budget to change out the window covering to correct the space mistake that makes. If the plan is to remove the counters then the color scheme is basically what you like. If the plan is to leave them then I feel the cabinets need to be painted. Because the cabinets are sort of stuck up all over, I'd plan to make them blend vs pop. That can be done with paint. To do that, I'd plan to pull paint samples of whole wheat bread color browns and creams. Hopefully you like those colors (that's always a factor). But with a travertine floor, especially a light one, those colors are logical. If there are extra floor tiles somewhere that would be very helpful to take to the paint store. The color of the floor could tilt the scheme one way or the other. If that's ok, then find a greyish brown (I'd try to avoid reddish brown) that works with the counter color well enough to make it look more related to the lower cabinets. Then I'd try to find a cream/ivory color that works with that brown and has the same undertone. I'd paint the walls and top cabinets in the ivory and the base cabinets in the brown. I'd do the trim in satin and walls in the same color but flat. Then I'd look for a window covering (with that scheme a natural fiber look would be good) that fills the entire window niche and install it right up under the top of the indent in the wall. I wouldn't get a dark window cover as that will make it look like a hole in the wall rather than blend-y. Changing the window cover will make the wall look much better when everything is done. (If there is budget, I'd change the window to fit the whole space first but that's not necessary).

I like #3. It has the most depth and incorporates more colors and tones so to me it would be easiest to change wall color with that as a floor ( blue, green, grey, white, etc). I think with the #2 brown floor and black cabs and appliances you would not want to keep the blue wall color but go to something liked a greyed tan, which seems a bit muddy and dark for a laundry. The first choice does not seem to complement anything else in the room.

I think I would rob some square footage from the hall closet and turn it into a walk in shower in the mud room I would add hooks and drying racks for all the wet stuff, boots, rain gear, umbrellas, waders, snow suits etc... You can also pop a kid or a dog in there pretty easy for a quick fix if needed. I put a narrow rack on the wall for dry shoes and boots. 4 lockers on outside door wall, be sure to have drawers for hats, gloves, scarves, glasses, goggles, ear protection etc... also have room in upper cubbies for helmets and ball caps etc.. I put in your stacked wash/dry and the 4'4" double drain board sink next to it. I would probably add a fold up/down shelf next to the wash dry for folding (on the outside of the shower wall). I only had the measurements you gave and no idea which wall is which or how wide the doors and closet outside etc were so this is just a rough draft...