In gimp, you will have to set the image settings to non indexed/full color/16bit/32bit (or the layer settings)

However, using gradients is extremely forbidden in pixel art.
Isometric does not always have to do much with "pixel" art. For example your triangle, there is not much pixel by pixel work in it. If you want to explore the non pixel art way of creating isometric images, you can use gradients, but you are not allowed to post those images here :)
Succes!

When it says to create a gradient, it means a smooth gradation between two colors, which you can do by hand well enough for anything. Using a tool to create gradients for you causes a huge number of colors to be added and means you have less control over how the image looks. You can make a gradient by hand by using dithering to create the illusion of midtones between your actual colors and by carefully picking a set of colors that're evenly distributed in lightness.

You can create a gradient just like monkey said: Get some colors, sort them on your cylinder and use some dithering (look it up) inbetween

There is no exact rule that says that your triangle is no pixel art. However when the filling part is larger than the pixel by pixel part, its often (by me) said its not 'really' pixel art. This is however just my personal opinion.

Is the wikihow article right??? it says

Learn to dither. Dithering is a technique that blends your colors together, making them look smoother, or just creating interesting textures. There are 3 types of dithering: Basic dithering, stylized dithering and anti-aliasing. You will only learn basic dithering here, but it is easy to learn other two thereafter.

• Basic dithering is a 2x2 checkerboard pattern that is created outside of the color to make it blend with the other, lighter color (or darker) color. You can practice dithering by applying more or less to the image. See what the results look like.
• Once you master basic dithering, you can move on to stylized dithering, which instead of a checkerboard pattern, creates a random pattern of dots held together. It is used to create textures and more effects.
• Anti-aliasing is used on lines to make them smoother. You will not need it in basic pixel art, although sometimes it can be useful.

Shaded ball: Before and After.

Practice shading and lighting. When shading objects, you must always consider the lighting point, or sun. Once you decide where it is, imagine that object is in real life and shade it the way it would be shaded in real life. Decrease lum value of a color by 30 and increase hue by 5 and shade the area in. Then, dither it so the colors blend. Now, modify the shaded color: decrease lum value by 30 and increase hue by 10. Shade the area inside the shaded area; however, make it small, like 2 pixels or so. Then, dither. Now, depending on what material you're drawing (shiny or not), you need to add in lighting. This is done by increasing original color by 40 or 50 (whichever one looks better) and drawing a line or a little circle opposite from the shaded areas. It has to be about 2 pixels away from the outline and it should look real. Again, use dithering to fit it in.

Edited by hyperhopper - 25 September 2008 at 7:47pm

so let me get this straight, no tools besides pencil and fill, and to dither I cannot use gimp's dither gradient, or gimps color A to color B graidient, and you must do it in those patterns?

no to contradict you monkey, but I think gimp has a gradient which uses dithering instead of adding colors, if this is true, could I use that?

for once the internet saves us from WallofText.mod

thanks you internet

he could use it and then see what awesome dithering techniques the computer uses, study them and then use them in his pixel art right?

agreed, that doesn't look very good. i think this poor fellow would be helped out a lot if someone provided a link to a decent dithering tutorial (it would help me a great deal, too), but i think the real problem here is that the man thinks that the fancier tools that come with programs are what makes up most pixel-art. i'm definitely not an expert when it comes to making pixel-art, but from what i've gathered, the good artists do everything, or almost everything, by hand, in fact that's one of pixeljoint's rules: NO GRADIENTS. it all has to be done manually, and i think that's what this person doesn't get.