Colour channel effect?

[Kalleheikki Kannisto]

1) Copy and paste the image onto a new alpha channel
2) Make a layer and fill it with red
3) Make a layer and fill it with blue
4) Load the alpha channel as a selection and create a layer mask for the blue layer

(You may need to invert the layer mask)

[Jackson Murphy]

Gradient map
1. Add “Gradient Map” adjustment layer.
2. Blue on one side of gradient.
3. Red on other side.
4. Done.

[Lee Tatham]

Thanks Jackson,
that method works perfect

Thanks too Kalle for an alternative method