I'm using Wilton's gel dyes right now.
Last night I was trying to get a dark blue bc, and no matter how much blue I added I couldn't get it dark enough. I even added black and it turned it kinda funky blue. I've tried added the Wilton tube colored icing when trying to achieve other dark colors, like a true red color, and even then I couldn't really get the red I wanted.
Is there a certain dye that you recommend to get these nice bright/dark colors?
There will be many that will tell you to get Americolor colors.
I use both them and Wilton, but I have been able to achieve dark bold colors with Wilton's colors.
I find it helps if I start with a thicker consistency of buttercream. For a 1/2 of a cup you need to add about 1/4 to 1/2 teaspoon of coloring. Skip the toothpicks and use something that picks up more color.
I recommend using Americolor gel colors they are more concentrated than Wilton's. Also keep in mind that BC gets one to two shades darker with time. So after mixing the colors wait 24 hour to get the true color. When I want to do dark colors I color my BC a week in advance & freeze it. IMO freezing also helps in bringing the color out.
Chefmaster liqua gel is highly concentrated and you use very little to get vibrant colors and there is no waiting for it to intensify.
I have a suggestion for dark colors. When I need to use them, I cover the cake as usual with uncolored frosting (usually IMBC). I then lightly skim coat the actual dark color onto the cake. This way, the guests don't get a mouthful of dark frosting to color their teeth.