How to check:
Categorize the different types of color-blindness (red-green, blue-green, etc), then: 1) find people with these conditions to review your slides, 2) use an available digital tool, or 3) use the poor-man's solution and print in greyscale: if any touching-colors are relatively similar, create more contrast.
If you're asking how to color-blind-proof your slides, the answer - if your primary concern is readability, rather than aesthetics - is two relatively simple rules (though the implementation could be more complicated).
- Outline everything in a colorblind-safe color that contrasts with the item outlined.
- Do not refer to things in your slides by color.
If your text is black and is outlined in white, it will be perfectly readable, regardless of background color (assuming their vision isn't particularly blurry as well).
You could extend this example to diagrams and graphics too: put a green square inside a red circle and they might be indistinguishable to the right people. Outline the square in white, and the shapes will be perfectly distinguishable, even though they can't tell which is red and which is green. Thus, rule 2 (above) comes into play: don't refer to things in your slides by their color.
The key is really to know your audience and address them appropriately:
If you suspect an average-population-density of color-blindness in the crowd, and have a small sample (crowd), you have little to worry about.
In the case of a small sample where you know a color-blind person will be attending, it would be considerate to determine their particular condition, and modify your slides to account for it.
If dealing with a sufficiently large crowd with suspected average-population-density of colorblindness, the rules above should suffice.
If addressing a group of color-blind folks of any size, I would go overboard in generating contrast in my slides and avoiding color-terms in my statements to make my presentation more understandable to them.