Rose,
The blue gene (Bl) causes the black color in a bird to be diluted to a blue color. In order to have a blue bird, you have to have a genetically black bird. For example, a chicken that has two extended black genes (E/E), like a black jersey giant, will normally be black but if a bird has a Bl gene and has (E/E) then the Bl gene causes the black to be diluted to a blue color. If an E/E (black) bird has two Bl genes then the birds color is diluted to the point it is almost white with the splashes of blue.
The blue gene is an incomplete dominant gene. The blue gene is not completely dominate if it were then the one blue gene would cause a bird to be white or splash. If you think about it, the E gene is still being expressed because the bird is gray and the blue gene is being expressed because it causes the black to be diluted.
The lavender gene, lav, is recessive. You always write a recessive gene in the lower case A chicken must carry two of the lavender genes ( be homozygous) in order to express the trait. One lavender gene will not express the lavender trait. When a bird has two lavender genes, the two genes work together to dilute black and or gold/red in a chicken. For example in the lavender wheatens that are being discussed on the board, the lav/lav gene will dilute the black color in the wheaten male and also dilute the gold/red and any browns found in the rooster.
The best thing you can do to learn genetics is to take one thing at a time. Make yourself a notebook with information about each gene or color. You can even define words or write anything you want. Write down the information in a way that you can understand. Then when you have a question go back to the note book. I have several notebooks I keep information in.
Rooster