User blog:Kooler186/Why Cyrax is Yellow. Unofficial but makes sense.

Cyrax is yellow because before Automation his mission was to spy on the Shirai Ryu. Due to the Shirai Ryu outfits being a way to mock the Lin Keui by being yellow instead of blue. So Scorpion could have sent him to go spy on the Lin Keui, at this time when he got back Sektor had clan members bring Cyrax to the automation chamber to be test subject number 2. Due to Sektor being the first volunteer, he thought if Cyrax would try to backstab the clan this is the only way to prevent him from doing so.