Query on Retaining the font color of a moving cell content and moving cell contents upward

Hi! I need some help. I have this program simulating the upward movement of some cells. My problems are:

1) The only red font should be "M", but in this case, the red font color stays on the initial cell position of the M. I need a code (or some way) to retain the font color of the "M" as it moves up.

2) There should be no "*" outside the 20x30 grid. After the characters move up, some * are left below the grid.

Here's my code:

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Thanks!