Hi!

Would be cool if you release it under something like CC-BY-SA or GPL2 license. I'm planning to make an open source Master of Magic remake, which has tower as a way to transition between worlds.

 I think the colors are really good, and the shading on the back adds good contrast :)

Pretty sure Graphics Gale does it.

Thanks for the feedback guys. I'll try and work on the advice given and I'll see if I can upload an updated version soon. Whats the best way to find out what colours are present to try and cut them down? Any program in particular?

 This is great. You have the talents, but maybe try a bigger project, just use a different color setup next time. 

 not too shabby, as Dr D said below try to pick better colors.

Not too bad for one of your first.

You should try to pick more itneresting color ramps. The dark cyan to light cyan ramp you have is pretty boring, try to spice it up a bit, change the hue some more. Light has color. I see you didn't just go up/down on the brightness slider and threw some greys in there too, but I think you could still push it a bit further.

Your interior lines are also too dark and you seem to use 5 hardly distinguishable shades to do it. (It all looks pretty much like black to me, at a glance.) You can save 2 or 3 shades there, maybe elsewhere too, but I'm not the best at that kind of thing either. (Your brightest 3 colors in the picture are sparcely used, and could be combined into one.)

Dithering is also a style choice, although it seems to me that it's been getting less popular amongst pixel artists lately. More people are trying to pixel without the use of dithering or too much dithering. In this case, I don't think it's really doing much for you here, you already have a healthy amount of colors to do this without dithering, and the end result would probably look better too.

Here's a quickish edit:
http://imgur.com/9HdJl

I removed a boatload of colors. I also removed the lightest highlight streak going down the surface of the tower. Don't think bricks should catch light like that, looks too shiny. Didn't touch the top part of the tower, that's why it's cropped so strangely.

It's a pretty different style from your original piece, and you don't have to be this drastic about it, but I think the issues still apply just the same.