Decals are overlaid on top of the sail texture -- exactly the same as you'd get with default layers in Photoshop or similar programs. So alternating white and transparent stripes could be colored
Since sails are complex pieces of equipment and we already provide a high-resolution sail texture for them, keep in mind that with sail coverage of about 50% or more, you'll want to make large decals somewhat transparent -- typically around 70% opaque.
You can preview this directly in your graphics program or using the
2D Content Previewer. NOTE: The previewer has a transparency slider, which is
not a supported game feature. While this means some color will show through if you layer e.g. a red decal on top of green sails, the effect is usually minimal in practice.
More info about what we're looking for in Flags & Sails can be found in the
2D User Content Guidelines.
Happy drawing!
