They do not look all that different to me, and I suspect they are both 70s.
Given the 70 and 78 were printed from the same plate, and with color distinctions so difficult to make online (what with the scanner, the processing SW, the various monitors, and then our eyeballs...), I think you need to get them expertised, side-by-side with reference copies under the same light.
It is my belief that the only difference is the paper and that requires having the stamp in hand and familiarity with the paper. I have never seen anyone on this forum indicate that color can be determined with a digital likeness of the stamp. There are some who might know enough about the cancellations to say they might help in making a judgement, however in your examples I do not believe there is not enough to form an opinion. I would appreciate other participants affirming my opinion and enlightening us as to any other way to make a solid determination.
yep, colors are hard enough in person and I know scanners and color profiles used when scanned mess it all up. in person side by side they do look to be different in color - a tiny bit. But I dont know enough about these to know for sure..... I may have them expertized for the fun of it.