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Not sure how to do this: I would like to set up a brush which would produce strokes close to white in the center, grading to color of choice (say, cyan) and then fading to background color (say, black) toward the edges.
It is something photoshop was designed to do.
Let's first create a custom brush do you don't modify an existing one. Create a shape for the brush - for example, use the marquee to make a long, narrow rectangle.
Fill it with any color.
Press Control-C (to copy the image shape)
Then select Brushes from the tool palette.
Under menu Edit, take Define Brush Preset. Give it any name you like.
Okay, you now have a custom shape to work with.
Open the Brushes Window. (Window - Brushes)
Select your custom brush.
Look to the left. All those options!
Try this: Click on the Color Dynamics box, then click on Color Dynamics an play with the sliders.
Do the same with Other Dynamics.
Now paint using that brush.
Cool, eh? Play with the color palette and other brush dynamics.
I hope you find that an attractive enough approach to pursue it further using Help Brushes.