extreme-g 2 on n64 fits many a late 90s "colored tat" trope, bonus points for that cheesy "3D" main menu UI as well, where they pointlessly displayed the attributes of each vehicle in a 3D circle. i guess hydro thunder is rather worth mentioning here as well, in terms of color scheme.
perfect dark came out at right the same time as deus ex and is cut from pretty similar cloth aesthetically, but with more flourish in terms of menu animation and the gimmick of the menu being a terminal that you can step away from and be ingame instantly. with timesplitters 2 i suppose they tried to go back to this UI style somewhat, after the awfully barebones first game.
on ps1 the syphon filter games come to mind for a cleaner take, the main and ingame menus have pretty distinct styles here. the animated borders in 2&3's ingame menus were somewhat memorable.
for that japanese futuristic style from the time as seen in PSO, digimon world 3's UI comes to mind. and actually from what i've seen, opoona really harks back to 1999-2000 despite being a 2007 wii release...