4759 was created as a bulky powder for original black powder rifle loads. It is VERY good for this purpose. However, the grains are very large and do not measure well. It will also bridge in a powder measure. You can minimize the bridging by filing the drop tube of your powder measure to an oval shape (Redding powder measure). It works especially well in cartridges varying from the 32/40 to the 45/70 in size.
I have never tried it in the .45 Colt.
Trailboss was especially developed to provide bulk in light loads for the .45 Colt and similar cartridges. It does this better than any other powder. The only downside I have heard, is it is expensive. I have NO personal experience with this as I have been completely happy with the old standards in the .45 Colt. For "standard" velocities and slightly heavier you can not beat Unique.
My "go to" load in the .45 Colt is 8.5 grs of Unique behind a 250 gr Keith bullet.
Dale53