Hello.. Hope u are well.. Its most likely genetics as sum pheno of gelato do have nice purple hues.. It cudb a cooler spot in ur grow space so effecting single plant bit more than others.. I noticed in pictures that ur fan leaves have brown and yellow spots wit slightly burnt tips.. This is due to slight over feed.. If its been warm the plants will drink more water than nutrient and leave ec higher than wot u put in.. Simply lower amount of nutrients uve been giving her.. They look great tho and im sure ull get a great yeild of quality buds.. Gud luck n stay safe.. 👍
Looks like it could just be genetics, but be careful because it does look similar to a phosphorus deficiency if it starts on older leaves first. Some of the others in the background look to have a calcium deficiency.