Hello reader!
If you don't know what the Rainbow mode is, I will enlighten your mind.
Rainbow mode is played with colored dices (red, green and blue) and uses the classic rules although there are a few differences. There are 4 extra fields. Those are Color Full House (purple house), Red Flush, Green Flush and finally Blue Flush.
The Red, Green and Blue Flushes are obtained by having 5 dices of their respective colour and awards you with 35 points. The Color Full House is awarded after having a combination of 2 dices of one color and 3 dices of another color (example: 2 green dices and 3 blue dices). This gives you a 15 points boost.
When you calculate the value of these new fields, the sum is 120 which is a fairly nice boost towards the 400 points you need to obtain. 280 points to go

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For those 280 points, I recommend going for the upper bonus (scoring a total of 63 points awards you with 35 points) and all bottom fields. You have to be a bit lucky with those 3 and 4 of a kind (having 4, 5 or 6's should do the trick) and with the Yahtzee, but all in all you should get there without real difficulties if you are lucky enough to throw the dices you need.
Additional notes:- Upon earning a joker, you score maximum points for any category in the bottom section. If all those sections are already closed, you will have to pick a field from the top. When you have to do the latter, you will score nothing so beware.
- If you score a yahtzee with dices of the same colour, you will get 200 points instead of 100. Pretty neat, right

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- To play this mode, go to Custom Games and select "Rainbow". The amount of players is your choice but off course playing solo will be a lot faster.
Good luck!

- MCoreBE