We had a spider crack like that on the lower bumper of our Axis. We ended up having to get it fiberglassed over and painted.
Here is the cracks/blister in the passenger side fog lamp recess:
The repair people said that it was going to be very difficult to match the base color of the gelcoat because of the fading. Instead they matched the dark brown stripes on the side (and thus gave us a very unique Axis, however subtle):
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