What interior wall color has been the most timeless?

Any shade of white has been the most timeless interior wall color.

vanilla or cream

Beige seems to go nicely, or a very pale yellow. Get paper samples and if you like one, you can get a small can of that color. Then try it on your wall near the bottom, let dry completely. You may want to coat it a second time, but most paint needs only one coat. Good Luck!

But ALWAYS paint your woodwork bright white to make everything else pop! We made the mistake of painting ours antique white once. Dreadful! If you like some color on your walls, Home Depot has a lovely Burnt Honey that makes wood furniture look warm, and white woodwork really pop. For more contemporary colors, there are some awesome grays that are popular - but I don't know how long they'll stay popular. If you like something more timeless, try Manchester Tan - Benjamin Moore I think. Looks great for a good neutral but has a good pop w/ white trim.

Tan.