How to display fibre bundles beautifully in mrview?

1

Hi,
When I use mrview when displaying more than two different tck files, the overlapping part of the two fibre bundles appears white what is the reason for this?

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Then my second question is how does my significance results file sig_fixels_05.mif file show up on the tck file on the glass brain, like the illustration.
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Thanks，
Astro