1. Give us the steps to reproduce the bug

I was playing Quick Draft Lorwyn Eclipsed. A few turns into a match the following happened.

During my opponent's first main phase, they cast Sunderflock. With Sunderflock's enter the battlefield trigger still on the stack, I tapped Tam, Mindful First Year to use its ability on my Mischievous Sneakling. The Mischievous Sneakling changed to all colors. Sunderflock's trigger resolved returning my Luminollusk and my Tam, Mindful First Year to my hand. The game progressed to the end of turn. At the end of turn, Mischievous Sneakling's colors should have reverted back to Blue and Black. Instead, Mischievous Sneakling remained all colors.

During my first main phase, my Mischievous Sneakling was still all colors. Also, the Vivid symbol on the Luminollusk in my hand indicated that my permanents in play were all five colors. At this point, my only permanents in play were Mischievous Sneakling, Lands, and Firdoch Core. When hovering my cursor over Mischievous Sneakling I could see in blue text on the card indicating that the color had been changed to all colors.

Later, I cast Tam, Mindful First Year. When Tam, Mindful First Year entered the battlefield, the colors of my Mischievous Sneakling changed to blue and black. Also, the Vivid symbol on the Luminollusk in my hand indicated that my permanents in play were three colors, Black, Blue, and Green.

1.   Note which platform you’re using (PC, Steam, Mac, Android, or iOS)
   

   I play on PC.

2.   Enter the actual results you’re experiencing
   

   A color changing effect that should have ended at end of turn didn't.

3.   Enter the expected results of the feature
   

   Effects that end at end of turn should end even if the source of the effect has changed zones.

4.   Add any relevant screenshots/videos
   

   I don't have any screenshots or videos.

5.   If you found a workaround, please add workaround steps.
   

   I didn't find a workaround. I don't save my log files.