Temperature Contour Map

I am trying to create a 2-D graph with three variables. The X-axis ranges from 0-24 in potential increments of 1/720's (translates into time of day down to as tight as 5-second increments), the Y-axis is 0-365 (translates into day of the year), while the last z-variable ranging from 0-100% in 1% increments. I would like to have this z-variable be a color gradient so that viewers could decipher the data based upon the gradient of the color rather than trying to decipher thousands of numbers, ultimately having the graph look like a countour map. Is this possible with Microsoft Excel? If so, how would I be able to do it?

Thank you

You might consider the surface chart.

One problem you will have is the 56 colour limit in xl2003.