First, you'll need an SVG of your image.
Right click your model, select “Add Modifier”, “SVG”
Select your SVG
Resize and mode your modifier where you'd like it on your whistle
Change the depth of your modifier; this will depend on your whistle model, but 1-2 layers is good for most images and color combos
in the “Objects” pane on the left, right click your modifier, select “change filament” and pick your other filament.