Hi,
you need to discard blood translucent pixels so you only set full colored ones.
Code:
for( j = 0; j < 32 ; j++ ) {
	for( i = 0; i < 32; i++ ) {
		if ( bloodSplatter1_pixels[i][j].pixa < 100 )
			continue;
		var pixel = pixel_for_vec( bloodSplatter1_pixels[i][j].pix , 100 , bmapHandle )
		pixel_to_bmap( terrainSkin , posVec.x + i , posVec.y + j , pixel );
	}
}


if you want to use translucent blood pixels, you will need to compute the resultant color before.

Salud!