Is it possible to discriminate tetrachromacy using sRGB color?
All the combinations of three sRGB primary colors are distinct for a trichromat. This immediately precludes any way to find out whether you are capable of more: if even a trichromat can distinguish all the colors, tetrachromat even more so.

But in principle, three colors are sufficient to check for tetrachromacy, but they can't be the sRGB primaries. The three colors you need must lie on one line on the chromaticity diagram, so that multiple mixtures of them could appear as the same color to a trichromat. Then a tetrachromat may be able to distinguish the two mixtures, which are metamers to a trichromat.