I seem to recall that there was a button for both minimum and maximum quality to accept trades within a range; right now there is only one.
I thought in the past that I was able to use multiple qualities (eg if there was a trade for gears->coins, it could be configurabled to accept only green and blue gears, while normal gears were ignored)

Am I mistaken or was this changed?

Additionally, I notice that placing the combinator will not respect quality: if I have a green quality hex and set a trade to be higher quality, the combinator defaults to normal quality signals