if you look in my sig their is a plant accident and emergency, i might of told you this all ready, click on that and have a look and compare your leaves to the pics in that thread, that might give you a good idea of what the problem is and how to solve it,
the leaf turning yellow and not going crispy could be down to lack of N, my lower leaves go like this either late in flower or if i have leaves that are not getting much light, they tend to fade from a nice green and go light green then yellow, so that either tells me is not getting enough light or if its late in flower then its not a huge problem, but if leaves start fading in veg or early flower then the plant may need a slightly higher dose of N, but check the link to the plant help guide and see if you can find something similar
you might even find the other problem their as well, ive not come across the 2nd problem with the grey/purpley type leaf yet, ill see if i can find out for you, king is also a good person to ask as he really knows his stuff, so he may of come across something similar himself or helped someone with a similar problem,
i just checked the plant hospital in my sig and their is one pic with a leaf with a black type problem on it, its coming up as phosphorous def, but check into it and ill see if i can find someone with a similar problem or someone who can give us some idea of what it is and how to get it sorted