OK in this one I'll show you how to create an image like this
The good old black-and-white-but-theres-one-thing-colored that everybody loves
First you'll need an image to work on, photos of flowers work great. Bonus points if it's a yellow flower.
Open the image up in the Gimp. Next create a copy of the background layer. Click on the icon I circled in the image below.
If you wanna act real pro, right click the new layer and select Edit Layer Attributes...
and change the layer name to mask or something else.
First make the new layer invisible by clicking on the eye next to the layers thumbnail and name.
Now click on the first layer, so that it's highlighted which means that's the layer you're working on. Following the instructions in my B&W tutorial
turn it black and white.
Now click the eye again on the mask layer (the background copy we created) also click on the layer so it's highlighted. You should now see the colored variant of the image again.
In the toolbar click Layer->Mask->Add Layer Mask
in the pop-up window click Black (full transparency)
and then Add
You should now see this in your Layers, Channels...
...and the image will be all black and white.
Now we start painting the color back. Make sure the mask layer
is highlighted in the Layers, Channels...
Now select the pencil tool
Since the layer mask is black you must paint with white color to get the original color back (does that make any sense?). The image above has white as the Foreground color
Using the pencil tool start painting the part of the image you want in color.
Change the size of the brush to have better control, bigger brush for the middle parts and smaller brush for finer ends of the petals. Use Ctrl-Z if you go outside the 'lines'. Zooming in on the image also helps alot, hold down Ctrl on the keyboard and scroll the mouse wheel forward.
When you're done right click the mask layer and select Apply layer mask
then right click the same layer again and select Merge down
It takes a little practice to get it perfect. The big problem is usually your hands are shaking or the mouse isnt very accurate.
As always, comments or cries for help are welcome. And I'd love to see your results.