(I'd highly recommend Photoshop with this one.)
What to note:
1) BEFORE you even start editing your + texture, go:
Image -> Mode -> Indexed Color... and check how many Colors there are in the picture. 256 is the max. Keep them in mind.
~2) NOW. For +1 texture, edit it accordingly.
3) After you're done editing the picture, go back to
Image -> Mode -> Indexed Color... and put the Colors EXACTLY (or lower) than the original Indexed colorings. (If the New Indexed Colors are already less than the Original Index Colors, don't worry about it.
)
~If the Custom Colors ARE bigger, simply go to "Palette: Local (Perceptual)" for best results. MAKE SURE the "Transparency" box below remains UNCHECKED, and the
Options below that read:
Matte: None
Dither: None
Amount: [blank]%
[]Preserve Exact Colors (unchecked)
4) "Save As..." a TARGA picture and replace the original file with itself. (Don't know why it just doesn't save when you Index the picture.)
And that's all there is to that.
You INDEX the picture after editing it, making sure you don't go over the ORIGINAL COLORS, and Save. No sweat.
~2) NOW. For +2 textures, edit accordingly.
There are two ways of editing +2 textures.
1, if they do NOT have transparency, then you would follow exactly as described above.
2, if they have transparency, which you would follow the steps below.
3) After you're done editing the picture, go through the same steps as mentioned above for +1 ^ on Step 3. What you do different here, however, is making stuff Transparent. What you need to note, other than the Original Colors, is where Transparency may be. Not all +2 textures have transparency (certain characters like DK and Ike have it, though).
To check, simply go to the Alpha Layer, under the "Channels" tab at the bottom-right of Photoshop. You should see the layers "RGB", "Red", "Green", "Blue", and "Alpha 1" respectively. Check the Alpha. If it has black (or white; differs), the picture has transparency.
For best results...
4) Highlight the transparent area with the Quick Selection Tool (looks like a weird wand-pencil-stick, on the left toolbar in Photoshop).
~Go back to RGB Layer (with color).
~Index your picture accordingly, this time keeping AT LEAST 1 number below the Original Index, NEVER on it.
5) After Indexing, go to "Image -> Mode -> Color Table..."
You'll see a bunch of boxes with a lot of colors... Then you'll see where the colors end, and a bunch of blank boxes are open. Choose a blank box, input "ff00ff" (also known as "Magenta", #ff00ff) as the color, hit "OK", choose the color "ff00ff" as your color of choice in the Color Picker (one of two colored boxes at the bottom-left of your Photoshop toolbar), and... color in that selected space in your texture with Magenta.
6) After you've colored in the selected spot(s) with Magenta, you can now Save accordingly.
~Hopefully this works out.