If the OP wants to screw on one filter and "go" I'd go for orange but as I and others have said one colour doesn't fit all and you'll never know the potential for filters unless you try the range

I'd buy an orange and see if it does the job you want it to the way you want it to. If it does that's great and if not then invest in a bigger range such as at least yellow/green as well as the orange

pentaxuser