Photoshop: how to isolate a translucent spiderweb?

A layer mask as the first person suggested is a good idea. However, have you tried selecting the background rather than the web? Or is it just too hard to select? Another way is to use the pen tool to make a path around each area you want to remove (tedious, I know, but it may be a good approach). You convert the path to a selection (see the Paths palette, there's an icon that looks like a dotted circle, click on it to make the Path a selection). Also when you use the pen tool, there's a set of 3 icons in your options bar at the top, make sure the middle one is selected.

Once you've converted the path to a selection hit delete or backspace to remove it. Then command or control +D to deselect it.

I'd love to see the full size image, what little I can see in your avatar looks cool (I've got some cool spider and web photos too.)

use a layer mask and paint brush to color just the spider web the turn off the mask and cut the web to a new layer. it's easy