Blue: it’s believed that she’s named after Jay’s Blueprint albums but Beyoncé has posted poems/articles about the color blue in which they describe how the color relates to the meaning of life and it’s importance in the world. You can see that here: http://assets.gcstatic.com/u/apps/asset_manager/uploaded/2012/24/beyonce-tumblr-photos-1339752741.jpg
Ivy: for IV, or the Roman numeral 4. The number 4 has great meaning in their lives, i.e. Bey, Jay, and Tina were all born on the 4th of a month and Bey & Jay got married 4/4/08.