Adding a bit more indicator will not affect the results. HOWEVER, if you cannot tell the difference in the color of the 2nd and 4th tube in the picture on the Taylor website then there is something going on with your color vision, although the TA test is usually much more problematic for the colorblind to use than the CH test. The 2nd tube is hot pink while the 4th tube is sky blue. The colors are not even close!
And yeah, the test that Taylor uses is pretty much the standard test for calcium hardness and there test is actually one of the better ones that I have used (and I have tested calcium in both pools and aquariums).