Count it? Why? Transparency is like the anticheese. You have your chese, but then someone is bound to eat some, hopefully eat a pie-like shape of it, cause then you can have some anticheese, which is solely the absence of cheese. It's there, but it's not. That's the whole point. If the anticheese weren't there, the cheese would be, so then, logically, they're complete opposites.

Now, do you consider anticheese cheese? I don't, cause you can't eat it. It tastes a lot like the air and/or the fridge. And it's damn hard to put on crackers. it has none of the characteristics of cheese, so I refuse to call it such.

But you MAY argue that it says cheese in the name. FIE! I tell you true, it says anti as well. Not just anti, but an anti that precedes the noun in question. Meaning that it can't be exactly what it's not.

--HAHAHAHAHA! EAT LOGIC!--

And then point number three. Yes, points one and two were the same, but shut up, I need the really weird essay-like non-essay format. Please, don't get me started. Don't.

Anyways... Say someone had a harsh craving for some anticheese. You'd say "Well. That bit of air over there would do!" and you go and take a bite of it, only to realise you took a huge bite of anticheese. How was this air anticheese? It was waaay outside the cheese's parameters! Well, you see, essentially, the cheese outside the cheese's borders has precisely the same nonexistant levels of cheese as the anticheese, meaning they must be the same!

"EUREKA!" you cry. "This freakin' bloke's got some jolly well good ol' tea time logicalness in his -mumbling-"

(In real words, and sanely put, this means that, arguably, you can have no size to a picture, because transparency is not stopped by borders. So transparency is just like fancy cropping, and therefore not a colour."

Transparency, in the sense that we're familiar with as pixel artists, is only a representation (or lack thereof) of a certain color index... let's take GIFs or PNGs with binary transparency as an example (alpha channels are a tricky example because in that case transparency becomes another dimension in digital color space). In this case, you have your limited number of color indices (say 8).  They all have red, green, and blue components.  If you make one transparent, the only difference is that it is FLAGGED as transparent.  The color itself only becomes transparent in its representation; that is, if you specify it to be displayed as transparent.  Otherwise, the color is solid and viewable.  Heck, you can even see it in your editor; it's usually your background color.  If I go to my little Graphics Gale menu and tell it to count the colors, it'll count the color indices regardless of whether or not you can see them in the final product.  In a pixel/digital piece, I would definitely count binary transparency as a color, just because of the nature of the medium.

On the other hand, if I take my crayolas and scribble on the bathroom wall like I did yesterday, would I count the white background of the wall as a color, even if I had solid areas of white within the boundaries of the drawing itself? I don't think I would... I haven't thought about it much.

So I guess my opinion is that pixel = yes, traditional = no(?)

edit: to make things even more confusing, say you have two images.  One is just a black pixel.  Another is just a black pixel in the middle of a transparent canvas.  They both look the same and in nearly all aesthetic senses are the same image (unless you count the buffer zone caused by the transparency surrounding the second image), however, technically one is a single color image, and the other is a two color image.

Okay, maybe that wasn't as fun to think about as I thought.