Many people are surprised how easy this is if you have some textures ready to use.
I recommend using Paint.net, which can be downloaded here:
http://www.getpaint.net/download.html
I recommend this program for a number of reasons. The main one being that paint.net remembers settings you dial in so you can quickly apply them to other images. You will see why this is useful later. Its also less cluttered than GIMP, and also free.
Ok, so here we have some grass. We can do a number of things with it by going to the adjustments tab. Today we will look at hue and saturation.
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So as you can see here we can amp up the saturation to make the texture more vibrant
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Or move it more towards the green spectrum
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Or more towards the red for an autumnal feel
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Or off into another spectrum all together!
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So here I have decided to add a little more saturation, and movemore into the green spectrum to give the grass a fresher feel.
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So now if you have multiple textures you want to apply this tint to, just open them
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and navigate back to hue and saturation and PAINT will remember your last slider settings. Gimp does not do this.
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You can do this with all textures you have full perm access to, and its lots of fun experimenting. Now you can have your textures JUST how you want them. Often things are too bright, to dark or have the wrong hue, now you know how you can fix that.