I cooked 7 percent fat hamburgers today. Indirect 400 degrees heat.
When the meat was at 140 degrees I put them on my serving plate...Red and gross looking.
I put them back on the grill...400 degrees for 6 more minutes...
Meat was 160 degrees...Not gross but still red.
Were they red because of indirect heat...or did 7 percent fat cause it?

I really do not have a good answer just my opinion. First I doubt if cooking them in direct would cause them to be red however I only cook my hamburgers using direct heat with the temp at 350 or above.  Also the percentage of fat should not make a different although again I prefer a higher percentage 10 to 15 % as I think it adds more flavor. 

I also believe the quality of meat can make an impact but then again hamburgers cooked to 160 on a grill should not be red inside regardless of quality and the outside should definitely be brown.  sorry I could not be more assistance maybe others will chime in

The meat will react with the smoke and have a smoke ring...I guess it is feasible that it could have gone through the whole burger.  If it reads 160° on a reliable probe it is done, so I have no explanation for the color either.

I typically purchase my beef from a friend who does all the butcher work. I ran out and bought some from the store that was like that. I don’t know if dye was used or what was going on. When I smoke hamburgers the outside will be reddish and a smoke ring, but the inner is still brown.

I cook mine at 250° for about an hour and they are usually in the 145°-155° range and still juicy just how I like them.  Beauty is in the eye of the beholder.

Red or not, I might try that.

I've never seen this.  I'm guessing smoke ring.

The reduced fat content equals greater meat exposure to the smoke.  How thick were they?

Very thin burgers..

Very thin burgers..

That reinforces my opinion that it's smoke ring.  I think it formed from top and bottom and met in the middle.

You make a great observation and point regarding fat content and smoke ring!  I believe it would intensify as the fat is reduced!

I've not seen that much "smoke ring" in such a short time at high heat. A stumper for me.  How did they taste?

Mike, where did you get your beef? Is there any possibility they added food coloring to old ground beef? Can supermarkets even do this? Zooming your pic, I can see almost no texture inside that burger, like it was ground to a slurry.

I know that colors are not particularly accurate on the internet, but close up, that burger does not appear to be very rare, more of a medium or at best, medium rare. 

They tasted great!
Also...No food coloring added.