vBulletin 3 and vBulletin 4 themes are 100% incompatible with vBulletin 5. Converting a vBulletin 3 theme to vBulletin 4 and vice versa is relatively easy, but to convert it to vBulletin 5 and making it look even remotely close the same is a lot more work.
If you really want to look/feel/colors of your vBulletin 3/4 theme, your best bet is to find someone.
https://vborg.vbsupport.ru/forumdisplay.php?f=30