I have some values, between 0 and 255, stored on an sd (can be in any format), which correspond to rgbw color values. There are too many numbers for the on board arduino memory.

What is the go-to method to extract these numbers into integers?

Your question is a bit vague. Are you concerned about changing bytes into integers? If so all you have to do is assign the byte to the integer like this:

byte RedByte = something read from memory
int RedInt = RedByte

255 (decimal notation) and 11111111 (binary notation) and FF (hexadecimal notation) are all the same number. You can represent the same number in different forms, but the value is the same.