An Ultraman's greatest weakness is his need for solar energy. The earth's atmosphere weakens the Ultraman the they stay. The Color Timer is a light formation usually on the Ultra's chest. The sunlight reduction means an Ultra can only stay on earth for 3 minutes. They do not have this problem in space as long as there is a light source.The Color Timer starts out blue, When the energy gets low, it starts to flash red. It gets faster and faster until it goes out entirely. If it goes out, this could risk the Ultraman death (The english dub of Ultraman where the narrator says, "If it is to go out, it will mean Ultraman will never rise again." was probably just for added suspense). On the Planet Ultra, the Ultra's do not have this problem there because of the plasma spark.

In some universes, the color timer does not act as a clock but a gauge on how badly weakened the Ultra is, such as the Nexus and Gaia universes. Also some Ultras have their color time not on their chest but their forehead similar to Ultraseven's beam lamp, for example the three ultras the comprise the Ultra Force.