What to check and what to avoid when you are choosing your strings.
The most important thing to check is that the twisting of your string is even in the whole vibrating lenght. No white spots, no open twist, no different angles. You can easily feel those by Mersenne's test.
What is less important is the color. Strings shouldn't be too white, it means they are bleached too much with chemicals. I wouldn't matter if they are yellow or brown, it is really just a matter of how they are cleaned, disinfected, and chemically treated. Brown strings can sound fantastic in the middle and basses, but I would prefer straw yellow for the chanterelles. Not too bleached, but perfectly clean.