
Rotten red as you mention could mean Extreme passion which often is not a good. For example yandere characters are like that extremely passionate and in love with their crush but don't care of their loved one's feelings. The "I'm doing this for our happy ending" but it's in truth it's for themselves...
Tho I remember I read in the raws that the color is not related to the ending but is an indication of "what kind" of feeling the character has for Penelope. The color changes since emotion changes... For example 4 some character it's "family love" (not incest. Platonic love), possessive love, etc etc.

I don't remember if it was mentioned in the webtoon but in the novel the protag specified that it's difficult mainly for other reasons too:
1) the amount random bad ends
2) playthrough as Penelope was an expensive dlc
3) very hard and unsatisfying so no one paid more than the first tries. it was a waste of money to players basically (to begin with Penelope wasn't a liked character too)
4) since almost all players did that there are no guides for Penelope stories which double the difficulty. Even reviving Penelope after a bad end ask you real money. Which is so bs (as an otome gamer myself I'm triggered haha)
5) it's a mobile otome with micro transaction we can assume its one of those pay to win otoge (like Story jar. The gem system is so trash and predatory no one played the game in the end and the app died).
6) the protag never (if recall) got survive after the coming of age event or finished/started any route since Penelope would die.
In this isekai vers:
- the hardship remains the same... Sinyeon (sorry ifwrote wrong) doesn't know the choices and answers or events after beyond the coming of age. Is asked to spend money for choices and random bs too.
It's so funny how I expected Eclis to act like this just because his heart color is weird. BUT MADZAM?!?!?! HOW DID PENELOPE NOT THINK THIS ALL THE WAY FROM THE MOMENT SHE SAW THE COLORS?!?!? KALISTO IS BRIGHT RED FOR A REASON MADZAM BRIGHT FUCKING RED UUHUHUHU like basic game logic is that if the color is pretty, there's a good chance its a good ending an example is Mystic Messsenger! Haiyaaaaaaaaaa