grimwerk: Now we know that at least one yellow and at least one red are in the final answer.
adaliabooks: Do we? We've got five of the six colours but how can we be sure (yet) which five are the right colours?
purple green aqua purple black blue
Answer: 0 black, 3 white
yellow purple green red blue aqua
Answer: 1 black, 4 white
The first two guesses share the four colors in bold. According to the first guess, the final answer can include at most 3 of those 4 colors. So at least one of those colors must be incorrect. As one of the bold colors is incorrect, red and yellow must be part of the five colors we know in the second guess.
We also know that black is incorrect, and that there is a maximum of one purple peg.