Could somebody tell me which is the paint code among these numbers:
31, 400-1, 5128 for an '88 245. These numbers were in the engine compartment, passenger side, above the wheel.

A guess:
400-1 Beige metallic/Gold metallic.

Assuming the vehicle generally looks gold, as I suspect it does, Shaye's exactly right. #400 was a very popular color during the late '80's, and you still see a lot of 740's out on the road painted that color. I think I had earlier seen the color listed as simply "metallic beige," but perhaps since everyone seems to take one look at cars painted this color and immediately characterize them as gold, the company may have changed the name.

As you now doubt have now figured out by way of deductive reasoning anyway, based on where the "400-1" appears on your vehicle, the paint code usually is on the second to last line of text that looks as if it's been typed into the form-like ID plate that's located under the hood at the very front of the car.

Maybe this link will help, typed in 'Volvo paint codes' on Google:


http://www.volvoclub.org.uk/paint_colour_codes.htm

That link doesn't work for me, but

http://www.volvoclub.org.uk/paint_colour_codes.shtml

--
-Matt I ♥ my ♂