Problems attaching coloured gel filter so ldr using Arduino Kit book & materials

This probably sounds a bit stupid. I am fairly new to using the Arduino and am attempting the Colour Mixing Lamp project in the "Arduino Projects Book'. Quite simply I don't see how I can attach the coloured gels to the photoresistors using the available materials - and the available space between the ldrs. I'd be very grateful for some help from anyone who has succeeded with this project.

I tried sticking sellotape to the photoresistors and now have something. Trouble is whatever I do the RGB LED seems to glow green or just very dim. I don't really know what's happening here.