Believe it or not, one may actually experience a slight yellowing of the eyes' lens with advanced age, usually long after one has joined the bifocal-wearing set, which will slightly diminish one's ability to distinguish the more subtle differences between grey, blue and violet. The less vivid of the blues and violets start to look a trifle greyish instead.
Out of 14 trials, which is the usual number for the Pseudo-Isochromatic Plates (PIP) and Ishihara tests, a person with "normal" color perception is generally expected to get 10 of them correct. Those of us who can get through a PIP or Ishihara test with zero errors are those whose color perception is actually better than the norm.
I wouldn't worry about scores like that if I were you; it sounds like your altogether normal in that respect. If it's any consolation, while I've got a corrected visual acuity of 20/12 bilaterally and can pass every color-vision test ever devised with no errors, I'm myopic enough that I'd fail a JAA Class 1 renewal and couldn't get a Class 2 except with a waiver (refrac: OD -6.75 s -1.00 cyl, OS -5.25 s -0.50 cyl and an uncorrected DVA of 20/250). Fortunately, my own country (the US) has a different set of rules!
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Anybody out after 2 AM is either a turd, a cop or a pilot. Or any combination of the three!