How to fix "sizes of input arguments do not match" error in OpenCV?

Question

C++ / C#

The error occurs when calling the weighted sum function AddWeighted (on the last line). The BLOCK_SIZE parameter is 100.

Scalar newColor = Scalar(0, 0, 0);
if (firstScore > secondScore)
{
  newColor = Scalar(255, 255, 255);
}
else
{
  newColor = Scalar(0, 0, 0);
}
Mat fragment = resultMat(Rect(j * BLOCK_SIZE, i * BLOCK_SIZE, BLOCK_SIZE, BLOCK_SIZE));
Mat color(fragment.size(), CV_8UC3, newColor);
double alpha = 1.0;
addWeighted(color, alpha, fragment, 1.0 - alpha, 0.0, fragment);

Error code:

What is causing the error? Perhaps the CV_8UC3 format is incorrect in this case?