You can either choose MSX1 or MSX2 as your Project Type.
This option affects your Exported data, and -
in the near future right now - the ability to change the palette.
MSX1 allows you to have a maximum of 4 sprites per line, where each sprite is of a single color.
So, to compose a drawing of, say, 3 colors, you'll need exactly 3 sprites.
In addition, the video chip in MSX2 is able to combine sprites colors with an OR operator, producing a total number of colors higher than the number of sprites combined. TinySprite take that into consideration and automatically generates the best combination of colors in order to minimize the quantity of sprites you need.
Note 1: the color 0 (zero) in MSX2 is not always transparent. In fact, you can change its RGB values and use it as a regular color. This behavior will be implemented soon in TinySprite.
Note 2: in MSX-BASIC you can change the sprite bitmap mask using SPRITE$(N)=[pattern]. With MSX2 you can also alter the line colors with COLORSPRITE$(N)=[attributes].