▁possess ▁ir id op hor es ▁or ▁le uc op hor es , ▁which ▁do ▁not ▁contain ▁true ▁p ig ments , ▁but ▁light - reflect ive ▁structures ▁that ▁give ▁ir ides c ence . ▁An ▁extremely ▁un common ▁type ▁of ▁chrom at oph ore , ▁the ▁cy an oph ore , ▁produces ▁a ▁very ▁v ivid ▁blue ▁p ig ment . ▁Am el an ism ▁in ▁fish es , ▁am ph ib ians , ▁re pt iles ▁and ▁birds ▁has ▁the ▁same ▁gen etic ▁et i ology ▁as ▁in ▁m amm als : ▁loss ▁of ▁ty ros in ase ▁function . ▁However , ▁due ▁to ▁the ▁presence ▁of ▁other ▁p ig ments , ▁other ▁am el an istic ▁verte br ates ▁are ▁s eld om ▁white ▁and ▁red - ey ed ▁like ▁am el an istic ▁m amm als . ▁ ▁A e um el an ism ▁Mel an ocy tes ▁depend ▁on ▁the ▁Mel an oc ort in ▁ 1 ▁re ceptor ▁( MC 1 R ) ▁to ▁signal ▁the ▁production ▁of ▁e um el an in . ▁L oss ▁of ▁mel an oc ort in ▁ 1 ▁re ceptor ▁function ▁or ▁high ▁activity ▁of ▁the ▁MC 1 R - ant agon ist , ▁Ag out i ▁sign alling ▁pe pt ide , ▁can ▁cause ▁the ▁w ides p read ▁absence ▁of ▁e um el an in . ▁L oss ▁of ▁MC 1 R ▁function , ▁a ▁re cess ive ▁trait , ▁has ▁been ▁observed ▁in ▁many ▁species . ▁In ▁humans