Yellow is going to be hard. For me it more of a soothing color then caution. My baby's room has a lot of yellow and when the sun hits his window the whole room feels warm.
When talking about flowers yellow means friendship, Right? DH thought that and gave me yellow flowers one time and told me that he knew that I knew he loved me but he want to show me we still had that friendship. I look forward to seeing what everyone comes up with.
I have the picture above on my backdrop for inspiration.