No I'm not (but I'll probably switch to this technique).

At first I used a 1x256 texture which stored the modified color for the 3 channels:
Color.r = tex2D(..., float2(Color.r, 0.5));
Color.g = tex2D(..., float2(Color.g, 0.5));
Color.b = tex2D(..., float2(Color.b, 0.5));

...but this wasn't good enough because when doing complex color modifications in gimp (which I want to look the same ingame)
output.red, for example, isn't only affected by input.red but also by the other channels. (I hope it's clear what I'm trying to say...)

Now I'm using a 2D texture (256²) like that: Color.r = tex2D(..., float2(Color.r, <average color>)); (for every channel)
So now the output color is also affected by the average brightness which gives a great variety.
It's still not as flexible as a 3D-Lut but easier to create and works pretty good.

Edit: I just switched to 3D-LUT because now I know how to save 3D textures and I've got a very easy way to create them while editing the screenshot to how I want the scene to be.