In 23w43a the Bat has a new model and texture. The old texture was mostly brown and black (see for example at https://minecraft.wiki/w/File:Bat_(Hang)_JE2_BE2.png), new texture is however only slightly brown and additionally purple.
This means, that the spawn egg, which has apparently not been changed, no longer matches with the color and seems quite off side-to-side (see below).
Can confirm. The old bat spawn egg uses the color from part of the old bat's wing texture. (Hex: 4996656)