Conditional Formatting

Select from C3:K44 and re-invoke conditional formatting, change the Applies to range to =$C$3:$K$45 and then select the condition and click Edit and change formula slightly to:

=$K3=INDEX($K$3:$K$45,MATCH(TRUE,$K$3:$K$45>=$M$1,0))

The $ forces all cells to look at column K for conditional check and format.