can't change colors

I’m trying to create an animation for a school project and I need to add a background so I use a color card. I select white and I create a color card but it comes outs black. When I try to double click the color card to change the color it said that it is already white. I’ve tried everything that I could think of but it always comes out as white!

please help!!!

Sorry if I’m asking something too basic, but Did you connected the colour card to the final composite module?
Can you see the coloured background on the camera?

Also, which edition of Harmony are you using? If you’re not using Premium, but Essentials or Advanced, try to select the colour card from the timeline, right-click and select ‘Connect to Composite’. Note that if you have your display in “Display All” when you create new layers they might be created disconnected from the composite, so keep it in “Display” or “Default (Display)”.

Luis Canau