Sim Daltonism 4+

A window to color blindness

Michel Fortin

    • 4.9 • 445 Ratings
    • Free



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 2.0.5

• Corrected an issue with the filter where some saturated blues would incorrectly become purple.

Ratings and Reviews

4.9 out of 5
445 Ratings

445 Ratings

Mimi Runs with Scissors ,

Huge Timesaver

Sim Daltonism is such a valuable tool. As of this writing, there has yet to be an accessible color palette generator that simultaneously checks for contrast and colorblind compatibility. Sim solves this problem: using a pallet generator that checks contrast (such as Adobe Color), place the Sim lens to overlap the palette half way, so you can see both the full color and colorblind view. This way, you can adjust the true color for contrast and be certain it is colorblind compatible—no more back-and-forth.

P.S. I'll add the 5th star when you release an Andriod mobile version. :-) Thanks!

gbbowers ,

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.

Mimi RunswithScissors ,

Terrific shortcut for designers!

I use Sim Daltonism to simultaneously check for colorblind accessibility as I create color palettes that pass WCAG contrast. By positioning SD's lens to stretch halfway across the row of swatches in the WCAG color palette generator, I can see how well they work for folks with CVD. No more jumping back and forth between separate checkers, tweaking and tweaking to get it right for both.

Bonus: It's also a great for teaching clients color mindfulness. "Umm, y'know, that chart makes your competition stand out more…" ;-)

App Privacy

The developer, Michel Fortin, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary, for example, based on the features you use or your age. Learn More

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