Posting the same answer here I put on the update post about this.
I want to acknowledge everyone who has indicated that with the new buttons it is harder to tell whether you have already voted on something or not. This is an issue that makes it harder to engage on the platform, which we take seriously. We saw that this problem was especially prevalent on the Meta sites because they use grayscale.
We just rolled out a change across Meta sites on the network, making it much more obvious to see that you have voted on a question or answer. Now, after you have voted the whole button should appear dark, rather than just the outer ring, with the arrow inside appearing lighter.
If you find a Meta site where the updated style is not live, please let us know so we can address it.
On the network sites (excluding Meta) the coloration of the voting buttons varies based on the theme of the site, so they don’t look the same everywhere. If there are specific sites where you are finding the same problem of visibility after voting, please let us know in the comments here.