I always do a yeast starter and always use the same recipe for a 1000 ml volume using light DME. One of the two flasks I have is exactly the same as the one in the picture.
I get the differences in color too. In fact, I just did two equal starters, both using WLP001 from unopened vials, DME from the same bag, and water from the same filtered water bottle for a 10 gallon batch and they came out in different shades! It may be due to boiling one longer than the other (I imagine at the low volume level even a little bit of extra heat means a lot). It could also be how heat is distributed/handled differently by each of my flasks.
Funny thing is, I don't recall noting the color difference before.