ODG green mesh pattern would be my pick, just don't put it down , you might lose it ! a member on here years ago, stix, had a cammo rifle he lost for half a hour when out bush after he leaned it against a tree
As for colour..... I think that would depend a lot on the rest of your gun..... I think any colour other than black on an all black gun looks silly,but if the stock was camo then a matching camo shield would look fine. If the stock is wood then maybe the peanut vented shield ?