(These themes are going to be in my ? ?Val'? Tr?n?e??, 0dd?, and End?? ? shop. But feel free to use them
Im not possessive or anything of the sort!)
You're characters theme colors? Perhaps for the log in screen instead of just 'Feral Heart' It could be something like... 'Sahale's Feral Heart'
You could also do a preschool theme, so it looks like little kids drew all over FH!
Or an apocalypse theme, eerie greens, reds, ect.?
Your county's colors and flag Example: 'American Feral Heart'
Elemental themes, fire, wind, ice, snow, rain
Environments, such as the rainforest, veins could be creeping its way across FH, add some rainforest animals as icons, and vwalla!
Hope I helped just a bit :3