“Gold” and “Yellow”
The word gold is derived from the Proto-Germanic *gulþą, which in turn was derived from the Proto-Indo-European *ǵʰl̥h₃-to-m, a nominal derivative of the root *ǵʰelh₃- “yellow”, “ green”, “ to flourish”. Proto-Indo-European had a much smaller color vocabulary than its modern day descendants, and included a single word that covered both “green” and “yellow”, which is a rather unusual - but not unattested - color term. Most languages with small color vocabularies will combine yellow with red, not green. But enough derivatives exist in Indo-European languages with “yellow” or “green” as their meaning to determine that the original root must’ve meant both “green” and “yellow”. The derivative *ǵʰl̥h₃-to-m was thus literally something like “yellow thing”.
Another derivative, using the e-grade, was *ǵʰelh₃-wo-s, which became Proto-Germanic *gelwaz. This became Old English ġeolu meaning “yellow”. /g/ before front vowels became the /j/ sound in Old English, thus ġeolu was pronounced something like /jeolu/. This became the Modern English yellow.