Choosing colors is an important part of designing your poster. Below are best practice suggestions for color choice, but you know your poster best. Just think critically about why you are using color.
Don't use more than 2-3 font types. This is the perfect opportunity to use some of the "allied" font options in the drop down. Avoid word art. Think carefully about the size of your font. All of your text should be readable if the poster is printed on a standard size letter sheet of paper. A good suggestion is also to use text blocks that are 8-12 words wide. Too wide it becomes difficult to read, too narrow and it is tiring to keep skipping lines.
Consider simplifying your methods (if possible) by using a figure. Although you may be able to take a picture of your experimental set up, a figure will be more "tidy" and viewers will be able to "read" it more quickly.
Coloring for Colorblindness this suggests accessible color palettes. If you have a color palette it will also show how it will appear for those with different types of colorblindness
Color Palette Generator Fast way to generate a new color palette. Press spacebar to shuffle colors, and once you have a few you like you can lock them in and the generator will suggest colors to suit.