My favourite apple variety is the russet (sometimes written with a capital R when describing a particular variety of russet eg Egremont Russet or Roxbury Russet). It's got a rough, greyish-brown skin, with touches of reddish brown, hence the name russet. (The skin texture is reflected in an old word for the russet apple - leather-coat.) The word russet is similar to the word rust, which can also describe a reddish-brown colour, but the two words have different histories.
Russet entered Middle English from French, which got it from Latin. The original meaning was a russet-coloured homespun cloth worn, as the OED puts it, by "country people and the poor". Indeed, another of the OED definitions of russet is "rustic, homely, simple".
The suffix -et on an English word usually indicates that it is a Middle English borrowing from French. Words belonging to this group include bullet, fillet, pocket, pullet, sonnet, tablet, turret and many others. In Old French, -et indicated a diminutive (masculine form - the feminine form was originally -ete, although it's -ette in modern French). So, pocket was originally a small bag, tablet a small slab or panel, and bullet a small round ball.
Rust is one of the oldest words in the OED, having been in existence since the early Old English period. The word has a Germanic root and there are cognates in other Germanic languages such as Frisian, Dutch and the Scandinavian languages. The OED thinks that the word rust may have also been pronounced with a long vowel sound in Old English, shortening later due to the consonant cluster following.