Individual differences in response time (RT) experiment - searching for the right test
In most individual differences research, subjects are additionally coded along some dimension, such as young/old, low/high working memory, normal/cognitively impaired. Without this, you’re simply looking at individual variation, which doesn’t seem to address any question (what is your research question?). If you simply want to look at variation in overall RT on a subject level, I’d construct CDFs of mean RT collapsing over color, or perhaps for each color separately.  This will simply demonstrate that people differ, and you’ll find the distributions adhere to roughly ex-Gaussian. If you mean to test differences between colors, you can use ANOVA or compare CDFs using K-S tests, but again there isn’t a clear research question here.