A Brush With Death
There are two ways to pick up on this quest: rumors and speaking directly with the quest-giver. At some point while wandering around Cheydinhal, you'll hear that Tivela Lysandus' husband, Rythe, is missing. This will give you a "Rythe Lysandus" conversation topic with just about everyone in Cheydinhal. Follow up on it to get a pointer to the Lysandus house (kind of catty-corner to the Fighters Guildhall). Follow it and talk to Tivela to find out that the disappearance is particularly strange because he was locked in his studio at the time. When you offer to help her find Rythe, she'll give you the key to the studio and you're off.
Open the door and you'll see an artist's studio, replete with paintings, paints, brushes, and all the rest of the trappings. The obviously missing thing is the artist. When you put your crosshairs on his latest painting, though, you'll see a door icon. Most strange, but open the door anyway.
You'll find yourself in a strangely colored forest, fairly close to the missing Rythe Lysandus. Once you get your journal update (Rythe has nothing to say until then), you can follow up on his conversation topics to find out that he had been working in his studio when a Bosmer broke in, stole his enchanted Brush of Truepaint and then entered the painting with Rythe following. The problem is that without the brush, Rythe is stuck in the painting and cannot return to his studio. When you agree to help, Rythe will provide you with six Turpentine potions that should help you with the Painted Trolls the Bosmer summoned up.
The Painted Trolls work just like normal Trolls with a couple of exceptions. They are always equal to your level with 25 health points per level and they drop "Painted Troll Fat" (Fortify Health, Fortify Magicka, Restore Health, Restore Magicka) rather than the normal stuff. The Turpentine is a leveled potion, too. It will do 20 points of damage from Levels 1-3, 50 points from Levels 4-7, 100 points from 8-11, 150 points from 12-15, 200 points from 16-19 and 250 points from 20 and up. If you work out the math, that means a single potion is never enough to completely take down one of the Painted Trolls, but it can put enough of a hurt on them to make them manageable. Those with good Sneak skills might be able to get in a ranged sneak attack, but six potions and six trolls means "caution".
The Trolls are spread out so you shouldn't have to take on more than one at a time, but they do wander a bit and it's possible to get two of them on you at once if you catch them close enough to each other (ouch). Rythe is essential for now, so it might be possible to lead a troll back to his area to get a little help if you need it. He doesn't have any weapons, though, so it's an iffy option at best.
When you reach the last one, you'll see the dead body of the Bosmer and can collect the magic brush after taking care of the Troll. If your Acrobatics skill is high enough, you can bypass all but the last Troll by jumping up the rocks right behind the point where you appear and climbing over.
Return the brush to Rythe and he will paint an exit back to his studio. After he talks to his wife, he'll thank you and present you with the Apron of Adroitness and a 1-point Fame boost. The Apron has a leveled boost to Intelligence an Agility. If you have any Turpentine left, just sell it. It won't work on anything except Painted Trolls.