Bottom big leaves turning dark black/brown

I have 2 pics. One is from a week ago and i checked on my 1 plant and i noticed about 5 of the biggest leaves were this reallly dark color please help.. i dont know if it is something wrong or its suppose too be like this and im just being a big noob

The purple leaves and red stems are more than likely due to a change in the plant's climate, colder evenings. If not, it could be a P def, but the leaf's cell structure looks fine. How do the tops look?

The top looks the same except the Buds are growing bigger and the cola (?) is starting to grow.. everything looks perfectly healthy except for those 5 big leaves that are brown... but where ive lived its like 40 to 50 degrees in the morning and like 60 to 70 in the afternoon... and today it is like 90 out.. so they must be confused

o and sorry im colorblind so it was really hard telling what color the leaves were