Yes they appear very close out of the box,
however... I've recently been fortunate to work on coloring a film shot on Alexa, which also has some scenes shot on RED and I color my own Blackmagic footage. They all look very close..but start grading them and Alexa really stands out FAR above the rest. Coloring different looks on Alexa is like dropping a round peg in a round hole, it just fits right in, slides right down...and do the same with RED and Blackmagic, and that peg is like, oval,
kind of eventually fits, but man you really have to shove it in there.
