Issue with Dropdown values using Axlsx gem

I'm trying to populate a list of values in the dropdown of excel using axlsx gem in rails. It seems like all the values in the dropdown are being displayed in lowercase.

 wb = xlsx_package.workbook  
 wb.add_worksheet(name: "sample_data") do |sheet|

  sheet.add_data_validation("A2:A1000", {
    :type => :list,
    :formula1 => "Red Orange NavyBlue",
    :showDropDown => false,
    :showErrorMessage => true,
    :errorTitle => '',
    :error => 'Please use the dropdown selector to choose the value',
    :errorStyle => :stop,
    :showInputMessage => true,
    :prompt => 'Choose the value from the dropdown'}) 
  end

In the dropdown, the values are appearing as red,orange,navyblue.

Is there a way, by which I can display the data as it is without the conversion to lowercase?(Red,Orange,NavyBlue)

Any level of help is appreciated.