post/spider.json changes post/blit ColorModulate uniform from [1,1,1,1] to [1,0.8,0.8,1], making it red. Previously when using that program again elsewhere it would use the default value in the post/x.json, but now it keeps whatever post effect overrides were done previously until they're overridden again by another post effect.

This means post/blit in post/invert.json for spectating endermen or post/transparency.json for Fabulous Graphics has the same red ColorModulate uniform applied after spectating a spider.

See postshaderuniformbug.png for a visual comparison of the enderman shader before and after spectating a spider.

See javaw_9GgvnisUf3.gif for a demonstration of the spider tint persisting with Fabulous Graphics.

Note: This happens with all post shader uniforms, but the spider shader is the only place where it can be observed without resource packs.