It is certainly possible to query the cell colour in an excel spreadsheet from matlab (only on Windows, with Excel installed) however you will need to be familiar with Excel object Model. In addition, there is no function in Excel to find all the cells of a specific colour, so you'll have to loop over the cells and query their colour one by one.
If either of these is an obstacle, I would suggest that you find a different way of defining your cell range.
Here is an example of how to query the colour of a cell:
filename = 'C:\somewhere\someexcelfile.xlsx';
sheetname = 'SomeSheetName';
cell = 'A1';
excel = actxserver('Excel.Application'); %start excel
excel.Visible = true; %optional, make excel visible
workbook = excel.Workbooks.Open(filename); %open excel file
worksheet = workbook.Worksheets.Item(sheetname); %get worksheet reference
rgb = worksheet.Range(cell).Interior.Color;
red = mod(rgb, 256);
green = floor(mod(rgb / 256, 256));
blue = floor(rgb / 65536);
workbook.Close;
excel.Quit;
