nostr:npub1uxeens8826rt5tdrd38hdtnvpw3eyfckln290q384qxu9t7zeu2q2qnf3d Hi, you can change the hashtag color using a custom theme. (Mona Settings > Appearances & Themes)

You could also just install these themes:
Classic Hashtag Light: mona-cat://7599
Classic Hashtag Dark: mona-cat://8ef7