Verse Gn25-30:34 discussing the food Jacob gave Esauv, who had come home hungry from a hunt, states. And Esau said to Jacob, Feed me, I beg you, with that red red; for I am famished; therefore was his name called Edom [ruddy] Jacob had given Esau bread and a pottage of lentils; and he did eat and drink, and rose up, and went his way; thus Esau despised his birthright.

In Rule1120, Rule #7, Formatting we have explained that the repeated underlined word red red means intentionally red. Then in Rule 1120, rule #9, Spreadsheets we have explained that it is reasonable - based on the age of Esauv and Jacob at the time of death of Grandpa Abraham and the conversation of Jacob and Esauv which is typical of teenage years - to assume that this whole incident happened during the week of mourning for Grandpa Abraham. It is then plausible that the lentils were intentionally red because red lentils are eaten during the week of mourning.

We now explain specifically how red is symbolic of mourning and also more generally we explain how the shape of lentils is symbolic of mourning:
1. Red symbolizes the blood and life which is now lost and departed;
2. Lentils are circular symbolizing the circular physical life cycle - starting at birth, rising in mid-age, and ending in death
3. Lentils are closed objects without punctures symbolizing the muted helpless silence of the dead.

Advanced Rashi: Rashi only mentions bullets #2 and #3. We have supplemented Rashi with rule #1. The symbolism, red equals life which is now lost is obvious. Also the verse explicitly mentions the redness, it even repeats it, to emphasize that the redness was intentional. So indeed we must explain it.

Rashi however left it to the teacher to explain the obvious (red=life) and instead explained the non-obvious, the circular and closed nature of lentils. We think this approach - viewing Rashi as explaining the non-obvious and supplementing Rashi with the explicitly stated and obvious - is a proper approach to enriching Rashi.