Why is yellow color always associated with Lord Krishna Janmashtami- following are few reasons:
Firstly in Shrimad Bhagwat it is mentioned in every description of divine Lord Krishna, the Yellow color pitambar is always described to be as bright as the rising sun.
Secondly as we hear yellow it reminds of warmth, spring or brightness full of cheer similar smile runs on face as you meditate about Sri Krishna or Shri LadooGopal. Thirdly the aura of Divinity glows as yellow and the flame of Bhakti in our hearts is bright as yellow thus yellow color connects us to divine naturally