I am by no means a Graphic Designer but try. I have an image I got from iconarchive and am trying to set the color to red (#840a0c) and setting transparent where there is white. I am using GIMP for this task and every time I give it a whirl I get jagged edges and it just looks awful:
Would appreciate any help.
The main problem in such an icon is the antialiasing zone between the black and the white.
@ybeltukov approach with GIMP is correct. In order to proceed and clear the white zone you need to select it (by color or with the magic wand) and tweak a little e.g. increasing the selection by 1 pixel and feather the selection to avoid the pixeling effect visible in your example.
In Inkscape is not so difficult.
At first you need to import the icon, while dragging it or using File->Import... (you can either embed or link the icon, for this example it doesn't matter).
Next step is vectorize the image, i.e. convert the pixels of the image in vertex and lines. This task could be performed using Path -> Trace Bitmap... (the icon must be selected). It appears a window with the settings:
You need to find the optimal settings for your image. With "Update" button you can have a preview.
When done, hit "Ok" button and close the window. The traced image is over the original one, as a group of paths.
Now, you can ungroup the image, choose the paths more close to your icon, edit a bit them (refer to a manual) and change the colors as you need:
Now, you can export the image (File -> Export Bitmap...) as a png (note that the inner of the image is transparent, now):
So... using GIMP or Inkscape? Depends of your needs.
Dead simple! Just put a layer above the logo layer with the colour (or texture) you want to apply to the logo layer below and set the opacity mode to screen and the edges will look nice and clean too.
I second what the other guys are saying about leaning Inkscape however!
EDIT: I just noticed that your original logo is dark grey rather than black so this method will give a lighter shade than the screen layer. You need to adjust the levels of this logo layer so that the black is fully black. I know the following screenshot is Photoshop but Gimp has a levels tool under Colours > Levels too and it's practically the same thing. Again, this is much better to do in a vector program.