I found a glitched spider. It seems to have a grass texture instead of the spider texture. The spider also doesn't have proper lighting, as it looks clear as day in a dark cave. Also, when spectating this spider, it has a blank black screen. I even checked on another mob nearby and the spectator feature is not broken, nor is it the lighting too low.

Also, as I was writing this the spider changed to a white spider, and I was in the pause menu. Spectating still doesn't work.

I have discovered that this also affects cave spiders.

Edit: before you ask, it is all spiders. including /summoned spiders.