Re-evaluate strategy for assigning channel colors

[mlinkert]

From ​https://trac.openmicroscopy.org.uk/ome/ticket/3651#comment:7:

Also need to review the color selection based on wavelength:

E.g. lei/joel/sequental scan 2/

• Currently cut-off red->green is 560.
• We have two channels with emission filters: 553-618 and 665-800
• We pick wavelength as cut-in + 15 (ignore emission).
• Both these channels are therefore colored Red.

Although the above example could be fixed by adjusting the "+15" > increment to cut-in or by moving the green->red boundary, this could > easily "break" another format / example.

Color selection algorithm could be improved to order channels by > wavelength - Preferentially color Blue -> Green -> Red, instead of > color 2 channels same color.

If it's not being done already, it would also be a good idea to do something with the Channel.Color attribute, as this is now populated for a handful of formats (see #3651).