Howard wears turtle necks, Raj favours a cardigan and Leonard likes his polos topped with an unbuttoned shirt. When it comes to clothing on The Big Bang Theory, consistency rules.
Sheldon, in this regard, is no different and can usually be found sporting a short-sleeved t-shirt over a long one with its sleeves rolled up.
There is, however, a fun theory that suggests the colors of Sheldon’s top layer tee is far from random. The theory states that Sheldon wears red when he’s angry, orange when he’s greedy, yellow when he’s afraid, blue when he’s hopeful, purple when he’s in love, indigo when being compassionate, and green when his willpower is strong.
Whilst this doesn’t always work, it’s a very convincing theory in many an episode.