Lottie doesn't make this easy for you. The file format is not intended for human editing / reading.
It's been a while since I cracked open the format to make sense of it — but I believe your colors are going to be in the format
"k": [1,1,1,1] (or from an example in your file:
"k":[0.9058823529411765,0.8901960784313725,0.8745098039215686,1]) — IIRC that's RGBA, with four values 0-1 to represent 0=>100% for each channel.
You can also poke around the internet for solutions folks have found to this problem.