Walmart Runs A Potentially Confounded Button Color A/B Test

Walmart just ran another iteration of a button color a/b test as part of their navigation tests (seen here and here). This time, it looks their team attempted to isolate the button color change (a yellow vs blue background on the search button). However, upon looking at this more closely we can see that there is a possible confounding situation. The contrast of the icon in variation's hover state has has dropped heavily (barely legible).

For all we know, such changes may already have tiny effects that are barely detectable (and therefore make no relevant difference at all). Nevertheless it might be good to check for such confouders.