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See https://files.catbox.moe/gxrxmq.JPG for reference.

The blue arrow was 99%+ fine, gambling on the very likely chance that nobody has a client with a blue menu background, but this isn't the case for white, black, and some greys.

As with good meme image text, it needs something like a sharp outline, drop shadow, or just a (rounded?) square block behind it.

Even then, the blue arrow fails in the case of placing a website link on a blue PC desktop or blue mobile home screen. Favicons generally just need contrast to be sure.