Its all your preference to be honest, a lot of people are doing 2
different materials now, its quite popular (I work at a company that
installs quartz and granite- the majority of my clients are mixing them
together). If you are going to do 2 different colors you can do the
island and bar in granite and the perimeter in quartz, or simply the
island in granite and match the bar to the perimeter in quartz- its your
choice, either one works. I wouldnt mix any more than 2 colors- would
be a bit too much going on then. And I wouldnt mix up the perimeter
colors either (the 2 long pieces should match each other)- the bar would
be the only exception to match the island because its a separate little
area. Doing all 4 pieces the same color would also be fine, just
depends on what you like- all in granite would be a little busier than
the 2 colors- so just depends on how busy you prefer- and then all in
quartz would be very clean and modern (Doing them all the same would
also eliminate your focal point- you wouldnt be drawn to one specific
area). Note: If you do decide to do granite on the island with a quartz
perimeter, especially if the granite is busier, make sure the quartz is
clean, a simple texture/pattern- you will want to focus on the granite
island then and not have the perimeter competing with it.

my perimeters and separate baking nook (much the size of your bar) are quartz and my island is granite. you might do your bar in either, based on which layout will save you the most money on your countertop budget.

my quartz is marble-lookalike and my granite is absolute black. my perimeter cabinets are white and my island is dark quarter sawn oak.