Paint one wall with lighter color?
Painting a room with a LIGHT(er) color will make the room seem LARGER. That's the only theory I know of about light and dark colors.
Use a LIGHT PAINT (not water) to lighten the paint. (Water will dilute the paint and weaken it.)
As far as WHICH color to pick, that's a personal choice. My best to ya and hope this helps.
Jay J -Moderator
If, instead, you mean "tone the shade of pigment down a few steps on the color slip" so as to change the pigment formula you add to the paint at the store, then doing so is an accepted method of reducing the impact of uniform colors that seem a bit "much:" most commonly extremely light or extremely dark predominent colors on expansive, unbroken walls with no doors or windows. It is more common to instead choose an entirely different but complementary "accent color" to break up the monotony of a very light or very dark (or overly uniform) predominent color.
I have done so in my bedroom in the reverse direction: painted one unbroken wall a sharp, vivid, dark, Mayan Red color to break up the monotony of the lighter, neutral shades on the other walls. It looks phenomenal and always draws a compliment. However, the very same Mayan red color on all the walls would make the room look like a cave. So you might try using dark paint on only one wall and stiching with lighter paint on the others.
Doing so can also be done where light hits different walls differently. Sometimes the exact same shade will look darker if the wall is blocked from natural light and the other walls are immuninated with natiural light. Same thing on the exterior for North (typically no direct sun) vs. South (lots of direct sun) walls: use a lighter shade on the North side than on the South side so as to create a uniform color appearance.
[This message has been edited by Lawrence (edited July 23, 2001).]
1. Diluting with water will not give you a lighter color, ie won't turn navy blue into pastel blue. BUT it will make an interesting change. You have a blue 'wash' which some people find attractive. Its a faux painting technique.
2. To lighten your regular color will take a lot of base paint. Get a gallon of the same base as your regular color. Then mix only 1 pint (more or less) of the regular color in it. You read it correctly. This isn't guess work. I had to do this with some paint my wife picked out for our kids' bathroom. After the first coat she realized it was too much. When I mixed it I thought a pint was not enough and added more. It was lighter, but not by much. In fact, start with a half pint and try that first.