First I downloaded Gimp. Once you have the software downloaded you can open up your image. One bit of advice... never work with your original file. I have two folders. One is full of my original digi images. The other is Digi copies. I always make a copy of the stamp I want to change and work from that. That way you're not permanently altering your stamp. You can continue to make copies and colorize those. Go to file, open and find your image. (which hopefully will be in a "copy" folder)
Here's my image once it's open...
Next, you're going to go up to the "COLOR" tab and choose "COLORIZE" from the drop down box.
You'll see a little box pop up. At this point a little trial and error comes into play. There's no right number to move the cursor to on the "lightness" bar. It's just going to depend on the color you want. This part determines if it will be bolder or more pastel.
Next, you're going to play around with the hue and saturation. Just move the cursor up and down to find the color you're looking for. You can see here that my hue is at 89, the saturation is at 34 and the lightness is at 53. This gave me a pretty shade of green but since it wasn't green I was after I kept moving them up and down until I found what I wanted.
I moved my cursor until my hue was at 0, my saturation was at 53 and my lightness was at 41. I liked this shade of red so this is where I left it.
Now that my digi is the color I want it I need to save it. Click the "FILE" tab and choose "SAVE AS" from the drop down box.
Once you click "save as" another little box will pop up. All you need to do is click "save". If you're happy with the name and storage location just leave it alone. This will bring up yet another box.
Click "save" here and this will save your new colored digi image.
It may seem like a lot of steps at first but it really is so simple after you try it a couple of times. It's so worth the effort! I hope this helps you. If you have any questions I'll try to answer them. If you decide to give it a try leave me a comment with a link to your project. I'd love to see what you created!