Lavenders and Coral Blue have the same base color (and both are considered blue gened birds, in the same color family), but the Lavender is fully pearled making it look a little lighter, and the Coral Blue is partially pearled making it look a little darker... and then there are all the other shades of Blue and Lavenders too with different names, lol. It can be really confusing when you are first learning the colors and what the markings mean. Head stripes are one of the major keys to figuring out who's what tho, and once you learn what all the basic markings mean, it's easier to figure it all out when you factor in the down/stripe colors too.
I've spent a lot of time learning the colors of keets and adults over the years, (I've stared at every keet/Guinea color chart I could find online until I was blurry, teary and cross-eyed, dozens of times!) and I have had lots of practice ID'ing my own keets (major understatement there), so I'm pretty accurate at it, lol. If you ever need help ID'n any, just ask and send the best pics you can take, I'll help if I can. (There are a couple colors that I'm iffy about, but usually I have a general idea what they could/should be, so I usually have an "it's either this color or that color" answer, and rarely an "I have no idea" type of answer on those, lol. At least i can narrow it down, lol. Sometimes it's impossible to tell from the pics no matter how many I see of the same keet/Guinea, so I have to give it a best guess then.