SXMS: Three(or more)-bean salad

This is a must-have for Christmas, along with a few other things to be posted in days to come. Probably because it's one of those "special occasion" type things that one tends to eat out of the fridge, instead of allowing to meld into marinated bliss...

3+Bean Salad

1 tin green beans, drained (or lightly blanch a couple of fresh ones for added crunch - sliced into short lengths)
1 tin butter beans, drained
1 tin baked beans in tomato sauce, slightly drained
1 tin red beans (sugar beans?), drained
1 large onion, peeled, halved and finely sliced
2 tsp snipped fresh parsley
(throw in a shake of dried mixed herbs)

Dressing:
1 tsp dry mustard/paprika
1/3 c white wine vinegar
1/4 c oil
2 Tbs sugar
1/4 tsp salt

Mix veggies, mix dressing and toss together - or just dump it all in a bowl, one ingredient at a time until it's all tossed together, after a manner of speaking. (Decide that doesn't look like nearly enough dressing, and add another batch or half-batch - optional)
Chill for at least one hour before serving, or overnight if you can resist the urge to eat it out of the fridge around midnight.

Note: most of my recipes are "add until it looks right" ones, so don't get anal about amounts. Size of cans of beans matters not an iota - just top up or coat with enough dressing to make you happy.