Brother GTX-4 Instruction Manual page 95

What to do when replacing RGB=255 with RGB=254
RGB=255 is identified as a transparent color. To a portion where RGB=255 is contained, no ink will be ejected.
In order for the white ink to be printed, select an area for RGB=255, and replace it with RGB=254.
To make such replacement, use the method mentioned below.
(1) On the menu bar, select [Layer] > [New Adjustment Layer] > [Selective Color], and create a new layer.
(2) Set the opacity to 20%, and click [OK].
(3) From the [Selective Color], make the following settings:
 [Colors]: [Whites]
 [Black]: 1%
 Mark the [Absolute] option
<TIPS>
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The method to replace RGB=255 with RGB=254 as shown above can be used only when the [Color mode] is set to [8 bit] of
[RGB Color].

For Photoshop, the action file "SolidWhite.atn" is made available in Useful Tools, which changes RGB=255 to RGB=254 (Refer
to "5-6-2. Action file for Photoshop >>P.118"). For how to use it, refer to the Help feature that Photoshop is provided with.
95
Creating print data