If not scarcer, the yellow examples always make a more battered impression because of their bright appearance. So a good looking yellow one is always more difficult to find than the less vulnerable dull colour versions. But indeed yellow generally is far from common on 4th type tippers, as it seems.

Two 'dull' tippers of mine:

Kind regards, Jan

I think yellow looks pretty good on the older models, but I don't have any either. But nice add to your collection in any event!
Terry

Exactly one year after this discussion came to a stand still, in 2016, I found this unusually bright yellow example, a 3rd type, with closed base plate: