Because of the fact that Jr. Pac-Man was on a much different hardware (essentially another modified Pac-Man hardware next to the Pengo hardware which is developed for Pengo from SEGA), Tim's skin color was slightly darker compared to both Clyde and Sue. This is proof of why Tim is NOT a brown ghost. Extra: The Commodore 64 version of Jr. Pac-Man also features a slightly dark version of Tim, this could be due to the Commodore 64 hardware itself. Reference: https://pacman.fandom.com/wiki/Tim