Three ways to set initial colors:

•   Color Picker. Click the short color bar under each color square to pick colors; it also accepts RGB/HSL/Hex values.
•   Base+Scale. Use the color picker to choose the first color (Base) and then enter two scaling factors in the textboxes under the next two colors and hit "Set". This puts the other two colors on the confusion line (under the selected blindness type) that passes through the first color.
•   Use Presets. Choose a preset from below.