153020

All the possible arrangements are: 1 and 3, 2 and 4, 3 and 5, 4 and 6, 5 and 3, 6 and 4, 4 and 2, 3 and 1.
The totals for these possible arrangements are:1 and 3= 36, 2 and 4= 52, 3 and 5= 68, 4 and 6= 84, 5 and 3= 60, 6 and 4= 76,
4 and 2= 44, 3 and 1= 28
The things that we noticed are: The totals are always in the four times table,
There is always a difference of sixteen between the totals of consecutive arrangements( 1 and 3=36, 2 and 4=52- these totals are sixteen apart), and the difference between the swapped arrangements are 8(1 and 3=36 3 and 1= 28 36-28= 8)
These things happen whatever the difference in the arrangements: the totals are always even, the higher the numbers shown on the dice the higher the total.
For all even differences: the totals are in the 4x tables and all the things said for the 2 difference counts for this.
The numbers 3 and 2 are needed (3 red and 2 blue) to make 42 (we used trial and error with all possible numbers for all differences).
Yes you can if you change it to have 6 red dice and 10 blue dice and use 3 as the blue number and 2 as the red number. 3x10=30 2x6=12 30+12=42