In my not so humble opinion: One of the defining aspects about the human species is our absolute need for taxonomy (heck, frogs may do it too, but I don't speak frog). We look for ways to describe things ((the "labeling" argument... as in "not doing it" cracks me up... as a species (who are part of a genus, which is part of a family, order, class, phylum, kingdom, and domain) we NATURALLY try and find order, groupings, similarities and differences in EVERYTHING. From cooking (spices, herbs, oils, sweet, hot, bitter, acids, etc.) to chairs, cells to medicines, art to architecture. Look ANYWHERE in life and we have systems of classification. Babies, toddlers, children, adolescents.... shapes, colors, measurements.... heck look at a college campus. Schools of similar subjects in colleges of an overriding subject, in universities.)) We SEARCH for patterns, we create them. They're soothing, invigorating, and absolutely NECESSARY.
Those who are unable to create or repeat those patterns as quickly as others (language, reading, math, movements, etc.) are considered delayed. Those who create or repeat those patterns faster than most are considered gifted. Those who are able to do it in ways most aren't are considered talented (artistically, scientifically, engineering, musically, etc.). Those who do patterns in ways that don't make sense to others are considered to have a disorder.
It's ALL about patterns. Social interactions, education, physical accomplishment... it's how we create or replicate patterns, how our brains perceive them, that determines out niche in society.
<grin> So I don't think ANY of it is quirky. :) I think it's human.
PS... The letters as colors thing has it's own classification it's call synesthesia http://en.wikipedia.org/wiki/Synesthesia
PPS... I have so many quirks I have my own "disorder", known as ADHD. But my actual talent with patterns happens to be human interaction... I'm a fiction writer. If this then this if in this situation given these variables and these backgrounds. Also known as psych classes are easy A's. And also known as I have entire worlds spinning in my mind at all times. People having conversations is the least of it. I have *hundreds* of "voices in my head" ;) at all times. I just happen to enjoy it rather than be disturbed by it. My son has something SIMILAR... but he uses it practically... which means that he's known as "charismatic" because he uses the patterns of social interaction in how he relates to other people. He's a raging extrovert and a natural "host".
I've noticed that 2 groups of people tend to "count" things (like flower petals, cars, etc.). Visual artists, and engineers. It seems to go along with people who have an innate sense of BALANCE.
LOVE this q :) :) :)