Hmm, not many yellow fish spring immediately to mind for me...
My Yellowtail Congo Tetras
Ram Cichlids (but a 180 may be too small to house two pairs of cichlids, especially when the Kribs would bully the Rams very easily, I suspect)
Forktail Blue-Eye Rainbowfish (which might well work with the bottom-dwelling Kribs, as these guys stay up near the water surface, would need something like 2 males and 4/5 females)
Bumblebee Goby (some ~2cm babies looked lovely at my LFS, but think they are brackish rather than freshwater)
Other bright coloured fish that might work in a Rio 180 that come to mind are...
Neon Dwarf Rainbowfish (needs at least 5 in group)
Pristella/X-ray Tetra (needs 5+ group)
Zebra Otos (develope lovely black/white stripes when settled in, but can be a bit hit or miss when it comes to acclimitising success, stay small at ~4cm)
Cherry Barb (needs 5+ group, regarded as very community friendly for a barb, plus they stay small)
Panda Garra (cannot recommend these enough, if my 3 are typical, very playful/inquistive fish in a trio. Will eat tank algae as part of their diet, like Otos, but grow to ~7cm)
Celestial Pearl Danios [Galaxy Rasbora] (small but lovely colourful fish, ought to stay in upper half of tank and so avoid the potentially aggressive breeding Kribs)
Denisons Barb [Redline Torpedo] (may get too big for 180l, as they can reach 15cm, but lovely placid shark-like fish, would really neeed at least a trio)
Celebes Rainbowfish (would need 5+, gorgeous green/blue stripes, orange/yellow fins, males have extra display dorsal fins)
That's about all my tired brain can come up with right now
