How to Create Perfect "Monochrome" Bitmap ? I Want to fill color in the Bitmap Image

Try this:
Create an object and give it a fill and a linear (for example) transparency.
Convert the object to Grayscale * bitmap with Transparent background (Bitmaps menu).
Change from Grayscale to Black and White (1-bit) mode (Bitmaps > Mode), use the Line Art setting.
You will get a bitmap that is faded from black to white, no visible transparency.
Now, here's the cool thing: You can change the colors of Monocrome bitmaps in Draw, just like with an ordinary vector object.
Simply right click a color to change the black part and left click to change the white.
If you left click the No color swatch, you will replace white with transparent and, voila!

* Also possible to use any of the other color modes, as long as you check Transparent background.