So what does this mean? It means that John thinks (and knows) that he’s mainly attracted to the opposite sex and that his same-sex attraction occurs less often. It’s interesting to notice that in many promo pictures from the stag night, John’s face is lighted up only in half with the pink/purple colour (and is lighted in half in purple during the conversation where he asks Sherlock if he has a boyfriend). Also the purple colour is used to code queerness and homosexual attraction, a colour used on the show many times, especially in ASIP, during the Angelo’s dinner scene. But the bisexual pride flag uses the colours in reverse: pink (same-sex attraction), purple (attraction to both sexes), and blue (opposite-sex attraction).
The colors are used like this: blue on the upper-space, pink/purple in the middle (just a tiny line), and red on the bottom.
The first shot is on John and the main colours : blue, red, pink, and purple. But it’s even better than that: the colours tell us exactly how John sees himself and how he perceives his sexual orientation regarding his feelings for Sherlock Many of us thought the lights in TSOT, where John spiked his beer (and Sherlock’s) with vodka, were the colours of the bisexual pride flag (thanks to who has been i think the first to notice this, days after the episode aired).
