One option, without VBA, but the workbook needs to be saved as an xlsm macro enabled book.
On the formulas tab > Name Manager > New > in Name put IsColoured > in refers to put =GET.CELL(63,INDIRECT("rc[-1]",FALSE)) > ok
Then in B1 put =IF(IsColoured,100,"")
Every time you highlight A1 you will need to re calculate the sheet for the formula to work