Thats the same as me. My eye colour changes from Blue to Green to Grey to Green-Blue to Green-Grey to Blue-Gray. I'm not sure when they change though, I only realize they have changed when I look in the mirror and see they're different from the last time I checked. Do yours change straight away or do they change slowly like over night?
On very rare occasions my eyes go completely (and I mean totally, 100%) grey. It scares people sometimes but it's only very rare.
It's quite quick most of the time. I typically can suspect without even looking. If my mood has changed somewhat drastically, I will sometimes turn to someone and say..."So what color are my eyes now?"
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It's faster for me, too, and also depends on what mood I'm in. If I'm more "Aquarius", to use the closest term I can imagine, even though I'm still myself, my eyes shift to green. When I'm more on the emotional side, like "Cancer", the sign I'm born under, they turn a degree of blue. I've watched them change back and forth in the mirror and figured this out.
Possibly, and let me configure (unless it's an obvious observation, then I apologize)... the energy spike set loose at the moment of epiphany ("awakening". my energy levels seemed to crescendo earlier this year, which is why I said "set loose") psycho-physiologically undercurrents every action with more intensity than "usual". This is what I gather, but I can only study myself, apart from those who may have different experiences and therefore gather different conclusions.