Fizzy, I've not seen the Red 600, but I just picked up my red 650 today. It's like a reddish orange color, maybe closer to a deep magenta. I wish I had a color swatch to take pictures and compare to. But, my red sticky notes look almost bright fire orange red compared to the 650.
Here..I've grabbed everything red I could find in my house. Probably a terrible comparison photo. But, I tried