I have a large group of objects that I want to apply a clipping mask to. The large group of objects are in different colours, so I can't make them a compound path. But there doesn't seem to be a way to apply a single clipping mask to them because you can only apply a clipping mask to 1 object, not a group of objects. So what do I do in this situation? See below for illustration of what I mean (simplified, this is not what I actually have, each flower is supposed to have different colour).
bring it (mask - new poly) in front of all graphics that you want to mask ( ctrl + shift + ] ).
select all that you want to mask and hit ctrl+7.
Note 1: if object have some fill and stroke it will lose it if that object became a mask (after ctrl+7). Steps 1 and 2 are for that reason...
Note 2: You can change background of mask by changing its fill color. Stroke, if given, will appear in front of masked objects (select mask with white arrow). This way there is no need for background object with simple fill (poly) and masking is done without steps 1 and 2.