The colour problems you see are produced because bias is not totally implemented.
I hope the next version will cover all video modes. It was funny to see the "gracha" mode working.
Also, Dave sound needs some effort on interrupts, to work with sampled sound, and to lower the playing rate, that is double as fast now.
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For me, all this work seems incredible, when one thinks that this is not a program emulating the EP, but a lot of discrete components(inside a programmable chip) making the same things that the custom chips.
So, in a future it could be possible to clone Nick and Dave following the VHDL code.