Joel is red-green colourblind. Joel also loves making things for his friends, especially food and crocheted goods. Joel is also extremely stubborn about doing things by hand without help.
What this means is that for the last decade, every year, Joel's various LGBTQ+ friends and family have received homemade, very unique Pride flag-coloured items from him. Such as:
The "wait, this is just aroace" rainbow cake for the first Hermit Pride event he attended (red, orange, green -> yellow, violet -> blue). Only Etho was knowingly aroace at the time, which of course led to a lot of jokes about Joel's obsession and memes for days along the lines of "Happy Pride Month to Etho and Etho only".
The "everyone now thinks I'm from the Netherlands" gay flag (green -> red). The recipient, Scott, will never let him live it down. As much as he loves teasing Joel over it as rivals, he still has the flag in his room, hanging proudly with the rest.
The "minion" nonbinary flag (purple -> blue) Cleo received. Except Cleo isn't actually familiar with pride flags either, so they spent a long time under the impression that the nonbinary flag was yellow/white/blue/black. Even after being corrected of her misconceptions by a horrified Gem and Scott, they still maintain that Joel's version looks nicer and she prefers using it.
The "actually this should go to Scott" bi flag (pink -> green, purple -> blue) for Gem. In fact, Joel thought that Gem's iconic green-and-blue outfit was entirely bi flag colours (instead of just her shoes), hence his choice of colours when he couldn't actually tell what the colour on top was. Gem did still keep the flag. In fact, it's now a running joke among the younger Hermits and their friend group that Joel is the official creator of the Gem Pride flag.
The "bloody murder" bi teddy bear (pink -> red, blue -> dark purple-black) he made for Lizzie. After, and despite all the ribbing, Lizzie loved it, declaring that maybe it really did fit the two of them best, given their shared proclivity for chaos, murder and a scene phase from just before they first started dating. She kept it in their room until their daughter was born and they "needed to make the room more child-friendly".
Even though almost none of Joel's pride gifts are ever the right colour (even with help, he will pick the wrong colour out of spite that people are actually offering him help), all the recipients love and treasure the gifts.