Rose leaves with pale patches

Two of my roses, For Your Eyes Only and a deep pink scented one next to it have pale patches in their leaves as though the colour has been sucked out. Does anyone know why? I saw something like this in a forum or gardening magazine, but I can't find it.

 

@Busy-Lizzie

A common problem caused by tiny rose slugs, which you will find on the undersides of the leaves, little white grubs.. they eat away the green..

 

Thank you @Mrs Hillard. For Your Eyes Only is very vigorous and is growing new leaves. I hope they won't be affected. The pink rose, it had a label saying "Baroness Rothschild" but I'm not sure, the pink is too dark, has suffered quite badly.