What are the dark lines that are on my roof?
Quick answer: They are "tramlines" -- wear marks running along the lines where the hood folds. Gritty dust gets into the fabric and abrades the fibres every time the roof goes up and down. The roughed-up fibres have a different texture, so they look darker. Cleaning and re-proofing darkens the rest of the hood and reduces the contrast, but the marks themselves cannot be completely removed.
The dark lateral lines on your roof are wear marks. The fibres of the fabric along those lines are roughed up and have a different texture to the rest of the hood, so they reflect light differently and read as darker. Because the colour difference is caused by texture, there is little that can be done to fix it. Even recolouring won't put it right.
What causes them
Gritty dust and pollen settle on the roof and work their way into the weave. Every time you fold the soft-top down and put it back up, those particles grind against the fibres along the fold lines. Over months and years the fibres flatten, fray and change texture. The marks always appear where the fabric creases -- so they line up with the geometry of the roof mechanism, not with anything you have spilt on the car.
Cars that are folded up and down frequently, and cars parked somewhere dusty, get it faster. A mohair roof shows them differently to a plain vinyl roof, but any folding fabric hood is vulnerable.
Can the marks be removed?
Not completely. A lint-shaver will tidy loose, raised fibres and take the edge off the contrast, but it only reduces the marks -- it doesn't erase them. Roof dye doesn't fix them either, because the colour difference isn't really a colour problem, it's a surface texture problem.
How to make them less obvious
If the hood is cleaned and re-waterproofed, the rest of the fabric darkens up to match, which closes the contrast gap and makes the lines far less noticeable. Cleaning also gets the abrasive grit out of the weave, so you're not grinding new wear in every time the roof moves.
Leave it alone and the wear keeps going. Eventually the fibres thin enough to tear and you get holes along the fold lines, which is a much bigger job to sort out than a clean and re-proof.