In the watercolor technique, you have to learn how to reserve whites in advance with the masking liquid and then apply the paint around it.
How to Use Masking Fluid
How to with Cass Art: Watercolour and Masking Fluid - Cass Art
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Using Masking Fluid (without ruining your paper), by Fia Sutton
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Tips for painting with masking fluid and watercolours, CreativeIngrid
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Playing with masking fluid : r/Watercolor