From the perspective of a color blind person, some colors are impossible to distinguish. Sim Daltonism lets you visualize colors as they are perceived with various types of color blindness.

Move the Sim Daltonism window over something on the screen and see what it looks like with a color blindness. With this app you can check the accessibility of websites and other user interfaces, make your visual designs better for color blind people, or just play around to better understand how various color blindness types affect color perception.

The Filter Window

The Sim Daltonism window acts as a filter for what is under it. You can click inside and manipulate windows from other apps that are located under it.

But you can change this so the filter window follows the mouse pointer, displaying the area around it. This makes it possible to view the filtered image alonside the unfiltered one.


Sim Daltonism is fast enough to filter a video in real time or to have many filter windows active simultanously.

If needed, you can reduce or increase the refresh speed to save energy or improve responsiveness.

Simulated Vision

Sim Daltonism can simulate the vision of many forms of color blindness:

• Deuteranopia (no green cones)
• Deuteranomaly (anomalous green cones)
• Protanopia (no red cones)
• Protanomaly (anomalous red cones)
• Tritanopia (no blue cones)
• Tritanomaly (anomalous blue cones)
All colors
• Monochromacy
• Partial monochromacy

Note that the colors shown are only an approximation. Color blindness varies from person to person and the simulator cannot represent everyone’s vision. Many other factors can affect the results, such as the automatic white point calibration of the camera. Nevertheless, Sim Daltonism is a good tool to better understand color blindness.

Sim Daltonism is open source and is also available for iOS.

What's New

Version 2.0.2

• Fix for dragging the filter window; this was broken on macOS High Sierra.

Ratings and Reviews

4.9 out of 5

13 Ratings

13 Ratings

Indispensable tool for checking design against CVD


I use and highly recommend SD to my design colleagues as it provides a completely independent and non-intrusive overlay to similuate how users with color vision deficiencies see the interfaces we're building, and if they'll notice the differences in state change.

My only problem with the app is that it doesn't seem to currently handle the dark mode in macOS correctly, which causes the icons used for controlling the type of CVD simulated to become essentially invisible (black icons on a black toolbar). It's an ironic oversight, and I kind of have to guess where the icons are, usually hitting the refresh-rate menu instead. Should be a simple fix, so I hope the developer can take a minute to update the app.

Developer Response

I'm glad you like this app, but I can't replicate your dark icon problem on my end. Please send me an email if you want to investigate this further.

An old standby lives up to its reputation

Mattinsky F.

I’ve long used SimDaltonism as a stand-alone app to evaluate how websites appear to those affected by many types of color blindness, and I’m glad to see it’s still around. Any time I use color, I like to do a quick run through all the types (by typing Command-1 through Command-9 in sequence) to get an idea of how differentiable the selected colors are to all users.

It’s an important tool supporting what should be a content developer’s highest goal: Ensuring content is equally accessible to all.



We are doing some accessibility testing for our site and this tool has been immensely helpful in choosing the correct colors for some important charts are graphs. The only issue I had was on multiple monitors it would crash moving between screens. If that bug is fixed this is a 5 star app for accessibility!


Michel Fortin
4.9 MB
English, French
Age Rating
Rated 4+
© 2005-2017 Michel Fortin


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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