It can be different for subreddit to subrredit. lol
technically the colors of the main reddit upvote/downvote buttons are "orangered" upvote and "periwinkle" downvote. However, in this particular subreddit they are red pill upvote and blue pill downvote. A lot of subreddits have their own style that is different. For example, /r/earthporn has a tree with green leaves as an upvote and tree with brown leaves as a downvote