Set a block of pixel colors.
colors array is a flattened 2D array, where pixels are laid out left to right,
bottom to top (i.e. row after row). Array size must be at least width by height of the mip level used.
The default mip level is zero (the base texture) in which case the size is just the size of the texture.
In general case, mip level size is mipWidth=max(1,width>>miplevel)
and similarly for height.This function works only on ARGB32, RGB24 and Alpha8 texture formats.
For other formats SetPixels is ignored.
The texture also has to have Is Readable flag set in the import settings.Using SetPixels can be faster than calling SetPixel repeatedly, especially
for large textures. In addition, SetPixels can access individual mipmap levels.See Also: GetPixels, Apply, mipmapCount.	// This script will tint texture's mip levels in different colors
	// (1st level red, 2nd green, 3rd blue). You can use it to see
	// which mip levels are actually used and how.	function Start () {
		// duplicate the original texture and assign to the material
		var texture : Texture2D = Instantiate(renderer.material.mainTexture);
		renderer.material.mainTexture = texture;		// colors used to tint the first 3 mip levels
		var colors = new Color[3];
		colors[0] = Color.red;
		colors[1] = Color.green;
		colors[2] = Color.blue;
		var mipCount = Mathf.Min( 3, texture.mipmapCount );		// tint each mip level
		for( var mip = 0; mip < mipCount; ++mip ) {
			var cols = texture.GetPixels( mip );
			for( var i = 0; i < cols.Length; ++i ) {
				cols[i] = Color.Lerp( cols[i], colors[mip], 0.33 );
			}
			texture.SetPixels( cols, mip );
		}		// actually apply all SetPixels, don't recalculate mip levels
		texture.Apply( false );
	}
    Set a block of pixel colors.
SetPixels above; it does not modify the whole
mip level but modifies only blockWidth by blockHeight region starting at x,y.
The colors array must be blockWidth*blockHeight size, and the modified block
must fit into the used mip level.