Clarification of the rules:

According to the source, there are a total of 4 rules:

A: All rows and columns contain the digits 1-9.

B: All 3x3 blocks contain the digits 1-9.

C: Within all 3x3 blocks, each mini-row (1x3) and mini-column (3x1) must contain 3 different coloured digits (1R, 1G, 1B).

D: Within all 3x9 horizontal bands and 9x3 vertical stacks, the same digit must be in 3 different colours (1R, 1G, 1B).

Rules A+B are standard sudoku rules and is equivalent to rule 1 of tso.

Rule C implies rule 3 of tso, though not vice versa.

Rule D implies rule 2 of tso, though not vice versa.

As for tso's colourblindness difficulty, you could still crack at these puzzles if you're willing to spend some time and effort. Just save all the pics in the web page (they're all 4-bit coloured png files sized <10kB each).

Now use a little windows accessories program called "Paint" to open them. You'll see a palette (color box) with only 16 colors. The 3 colors used (R, G, B) are respectively the 3rd, 5th, 7th palette squares in the bottom row of 8.

So just pick say, the red colour and use the "fill with color" tool to fill all the cells with R/G digits that you couldn't distinguish. Next pick the white colour and repeat the same process. Naturally all red digits will be wiped out and all that's left must be the green ones.

Now compare this to the original pic and you can spot the red digits. This time you could fill around the red digits with a yellow or gray background and voila, all 3 colours of digits could be easily distinguished now!

Also, seeing I could be the only one in this forum with some ability to read/understand Japanese, if you have doubt about rules of other Japanese puzzles, feel free to list them, I could help you clarify more. Ta.