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We calculate a player's "theoretical loss".  If their theoretical loss is greater than the transaction fee for the selected currency then we take care of the transaction fees.  For currencies like LTC, DASH, and DOGE playing 1 game at the equivalent wager of 1 USD will likely be enough for the transaction to be feeless, however since BTC fees are a bit higher, more play is required.  Let me know if you need more specificity.

As far a colors, personally I like them too (I'm biased) but I've had a few people mention that they'd prefer a dark mode, so it'll likely be a future option.

There are minimum amounts to wager, for example in BTC it's 1 bit.  However if an account has less than one bit, the player may wager below the minimum wager.  So likely in your demo play your demo account hit 0.16 bits.