Improve colors to 15 Bit RGB palette

[Stefan Rinke]

Instead of using 216 web colors palette, use 15 bit rgb palette with 32k colors

• display buffer / render buffer doubles
• use word instead of bytes for rendering
• adjust java tools for color reduction

see https://en.wikipedia.org/wiki/List_of_monochrome_and_RGB_palettes#3-3-2_bit_RGB