Is it new growth, on the end of a "branch"?

No, it's not new growth. It's on pre-existing leaves...not necessarily on the end of a branch...it's pretty random.

Some leaves have a golden/yellow tinge in parts and others a coppery red tinge in parts....

Also, I thought Wysteria was a climbing/clinging vine? While some of the branches have woven themselves into the trellis, other entire branches with offshoots never wove into the trellis....they are just leaning 'against it'. But as they get bigger, they may start to hang down a bit. Should I be trying to force some of the leaves in through the trellis?

Tx.

Wisteria is not a clinger, it's a twiner, and sometimes you need to help the twining get started. The branches wind around each other just fine, but you do need to do some of the initial twining around the trellis.

I don't know what the different color leaves could mean - it could be a build-up of the insecticide, which you really don't need unless you have seen insects harming the plant. You might want to post a picture of the leaves in the Garden Clinic forum here on GW.

BTW, it's Wisteria with an I, not a Y.