Do you know what caused the colour to fade - sun? traffic?
I'm not an expert but I understand that the last thing to be applied to the concrete should be the sealer which is to help protect the colour from fading due to sunlight etc. On some cases I think you can mix up the dye with water and brush it onto the concrete when the concrete is very dry and colour will be enhanced. Sealer would be needed afterwards. Consult an expert. You may get some help from