Identifying unknown solution with indicators. why is one pKa value ignored and how to treat negatives values?
As you noted, the $\mathrm{pH}$ is fairly close to 9.

It's probably quite different from the $\mathrm{p}K_{\mathrm{a}}$ value of $\alpha$-naphtholphthanlein because if you have any of the yellow acidic form around, the solution will take on a greenish tinge. One order of magnitude seems sufficient so, $\mathrm{pH} \geq 9$

The sample with thymolphtalein follows the same logic in that since we don't see any blue, there must be little of the base form, so the $\mathrm{pH} \leq 9$.

9 is very close to 8.8, the $\mathrm{pH}$ where we would expect equal forms of thymol blue. Indeed, $10^{0.2}\approx 1.05$, so both forms are present in solution in roughly equal amounts.

Further assuming that intensity of the two colors is similar, you would have a mix of yellow and blue, also known as green.