The white part is pretty useless, ... the "fire" came up because you mentioned an "opal with color play" look.
The fire will be in and around the colored portions, and is a matter of carefully examining your finds as you explore.
It looks like colors that seem like more than just color, but, colors that arise from deeper in the stone, and sparkle, or dance, as it rises up through clearer agate. Ie: it originates "down in the rock", and not simply surface color.
Fire agate can be very beautiful, and if you see it, you'll know it, especially if you can track down some richer samples.
It's worth digging for, if you get in a rich spot.
Sometimes fire will appear as folks grind down and polish a stone, but the good stuff, you'll know you're into it in the field.
Follow the fire, in your search, ignore the quartz, and only save the colored chalcedony or carnelian if you begin to run into large, very clear high grade samples that can faceted into gem/jewelry stones.