Help! My Roof shingles are turning black!

Get your checkbook out. Avoiding replacement will only end up costing more because of potential to have leaks indoors and indoor damage. Shop for qualified honest roofers. Get referrals

on an other note how old is the roof?

I found this from a quick Google search: https://www.todayshomeowner.com/remove-prevent-algae-stains-asphalt-shingle/

Don't let Lee frighten you. It looks worse than it really is!

The dark streaks are a type of algae that lives off the minerals in some types of roof shingles. Algae thrives in moisture, so it's seen most often on shaded or north-­facing roof slopes that don't get a lot of direct sun.

While it's true that algae doesn't damage roofing, it sure looks bad. To get rid of it, use a pump sprayer to wet down the roof with a mix of one part bleach to two parts water. Bleach will damage foundation plantings, so rinse them well with fresh water before you start and after you're done.Then scrub the surface gently with a soft window—washing brush mounted on a telescoping extension pole. Don't use a pressure washer, which could damage the shingles. Also, do this work from the safety of a ladder or from the ground, not by climbing on the roof.

To stop the algae from returning, mount zinc or copper strips near the roof ridge. Then, every time it rains, the water that washes over the strips' exposed edges will pick up ions from the metal and inhibit the algae from regaining a foothold. And when it's time for a new roof, look for shingles with algae—resistant granules and the best warranty you can find.

Depends on WHY they are turning black. Is the roof old and the pebbly surface is washing away leaving only the asphalt part of the shingles? If so, you need new shingles and fast before you develop leaks. Is it turning black in streaks over relatively new (less than 5 years old) roofing? Probably either some sort of algae (as William mentioned above). Is it on a part of the roof where gutters from a higher roof empty? Could be mold or rotting leaves or something in your gutters. Best thing to do is get someone to take a look at it up close (you if you're not afraid of heights and have the proper ladders and a spotter) and see if the shingles are in good shape. If the shingles are in good shape, then it's some sort of staining going on that might be able to be washed off gently.

That is mold. You can spray it with white vinegar and power wash it. If your roof is over 10 years old and/or the shingles are turning up at the edges, you need a new roof. The white vinegar will kill the mold better than anything else, don't let anyone use chemicals.

I have found wet and forget roof cleaner effective for my roof.

This article about the best roof cleaner https://sweethomeideas.com/best-roof-cleaner/ may help you.