Oleg,
First Off, I agree with the above.
Second, my ex besides being really good with decorating, was from a family of painters. Amazing how women perceive this type of thing. She also was NOT into wallpaper, only as far using it for border, and accent.
She took into consideration the size of the room, off-white colors such as Egg-Shell white makes a Room look bigger, darker can make one seem smaller. Natural Light, morning or evening, direct or indirect were also considered. Natural North Daylight is what is used to grade diamonds and gemstones for instance, same applies if one is going to do sewing, knitting, reading, paintings - any hobbies where light affects color and texture.
Incandesent, Flourescent, Fireplaces, Oil lamps, candles...all types of lighting taken into consideration.
Oleg you know all about the affects of lighting, shading, hues and all.
Taking in consideration Furniture, type of wood, upholstery, Period themes....etc. Her goal was to accent and bring out. Pick the colors and textures, a border, maybe even add/ remove/ change the molding.
For example, for relative of hers with a narrow, longish room going to used for Painting both Watercolors and small figurines, indirect morning light [North daylight] , took a off-white shade of white for one wall and "textured" every other stripe. It looked like wallpaper - it wasn't. Stripes were on the narrow walls,about 3" wide, alternated smooth and flat - horizontally- the narrow walls "appeared" wider. Different shade of the same color , the same stripes running horizontally. Room felt more "square" or "less long rectangles". Es[ecailly wit the use of mirrors used to "use the light to advantage".
First thing she said though when she walked into the room to when she was asked for suggestions - "get rid of the acoustical ceiling" . Smooth ceiling , or one with a very subtle design, like a small "dab of a curve " here and there".
She watched her daddy a painter as a little girl, then "saw" things and ask daddy to try it on folks houses...
I'd just watch and learn, ask the right questions actually quite educational and something I enjoyed doing with her.
She took some feathers I had felled during Dove Season to match paint , fabric and texture - to do a room once. Said the hard part was getting something to go along with the Red AA Hulls she carried in too. Yep- she did so too...*grin*