Prefix the layer command with a dash
-layer c 8 * [enter twice]
If you're not familiar with wildcards, the asterisk means everything. You could enter BOB* and it would change only the layers starting with BOB, or you could enter *WEAVE and it would change only the layers ending in WEAVE, or you could enter BOB*WEAVE and it would change only the layers that started with BOB AND ended in WEAVE.
a * is any number of letters/numbers
a ? is a single letter/number
a ~ is everything EXCEPT the following
entering
-layer c 8 *|cl?bm* [enter twice]
will change ALL XREF layers beginning with CL have ONE wildcard letter/number then the letters BM followed by any number of letters/numbers to color 8
