When I started my design work journey in 2015, for a few years, I was always annoyed about why the black in illustrator looked different from one file to another.
And the light brownish black would generally make me crazy. It would not fix even whatever I tried, but sometimes it would turn pitch black.
Man, I was not sure why it would happen.
This could happen in between files from illustrator to photoshop or in between illustrator files.
Then over time, I learned about the different color profiles and how these colors work interchangeably. I will explain all this to you in this blog post. Stay with me.
CMYK Black is Not Black
If the CMYK black does not look black and is a little brownish, then just use the rich black code, which is C= 60, M= 60, Y= 60, and K= 100. Also, change the color mode from RGB to CMYK of your document.
However, it may still not look PITCH black if you stay in RGB color mode due to how CMYK colors work.
Your computer screen will always show CMYK color a little brownish to match it with how it looks on print.
Color Mode in Adobe Illustrator and Photoshop
So in Adobe illustrator and photoshop, when you work, there is a default color mode you have to select when you create a new file.
Here is how you select it when creating a new document.

Once you select the color space you need and create a new document adjacent to the file name; the color space details will be visible.
In the below example, it is CMYK Color Space.
CMYK color space is typically used for printing and publications where you have to rely on the four types of physical inks to print the document.
These four inks are Cyan, Magenta, Yellow, and Key (Black). We use these colors and combine them in different ratios to create all possible colors.

Similarly, you will be able to see RGB if you have used a color space in RGB right after the file name.
RGB colors are used for digital media where screens, displays, and digital platforms are involved.
RGB is the red, green, and blue LEDs that combine in different intensities to create all possible colors.

Are CMYK and RGB colors interchangeable?
Now let’s move on to why it’s essential to select the correct type of color space when working with illustrator and Photoshop.
When you keep working in RGB Color Mode and are requested to convert your files into CMYK, they will always become dull.
This is because RGB colors do not translate perfectly into a CMYK Mode. Further, RGB colors are bright because they have their light source.
CMYK colors represent a print that absorbs specific colors and reflects others to create a color representation. To reflect this core difference, CMYK colors are always a little dull than RGB colors when looked at a screen.
This correct representation gives you a clear idea of how your print will come out.
What this means is that if you have an RGB Code and you auto-convert it into a CMYK Code, there is no way you can convert it back into the same RGB Code. There is no formula, just best-guess estimations.
Below is an example of converting an RGB value of R=14, G=124, and B=255 into a CMYK Code. The Code I received was C=95, M=51, Y=0, and K=0.
Then I used the same converter to convert C=95, M=51, Y=0, and K=0 into RGB again, and I received R=14, G=125, and B=255, which is not the same as the original RGB Value.

So it can be easily understood that these colors are not interchangeable.
Common Mistake:
When people work in illustrator or Photoshop and are asked to use CMYK colors by their printing company, they will keep working in the default color space.
They will just start selecting CMYK colors in the color picker dialog box. They will change the color from RGB to CMYK in the wrong place.

So it is always recommended to change the color space from RGB to CMYK before you work with CMYK Colors. To do so, Open File > Document Color Mode > CMYK Color.
Why is CMYK Color not Pitch BLACK?
So, if you are working with CMYK colors in an RGB Space, the blacks will always look brownish, as CMYK colors are a little dull compared to RGB Colors.
Why is RGB Black more BLACK than CMYK Black?
An RGB black is produced after the Red, Green, and Blue LEDs or light sources are turned off on a digital screen. It’s more like the absence of color. So they tend to look entirely black.
On the other hand, CMYK Black is produced by using only black color ink. The ink job is to absorb some and reflect other lights to create a color.
The black ink is supposed to absorb all light, but in reality, there is no object with 100% light absorbing characteristics to create absolute black, so some light will always reflect.
RGB color space will always show CMYK black a little dull brownish to show this characteristic.
How to Fix a CMYK Black to Pitch Black?
There are two ways you can fix this problem.
1. Change the Color Mode
The proper solution to this problem is to change the color space from RGB to CMYK by going to Open File > Document Color Mode > CMYK Color.
This will solve the color problem, and you will see a pitch-black color for your CMYK Color.
However, you will have to adjust the CMYK value to CMY being ZERO and K 100.
2. Change Color Code to Rich Black
In CMYK Color space and printing, a term is known as Rich Black. It is achieved by keep the CMYK value as C= 60, M= 60, Y= 60, K= 100.
Rich black CMYK color will look pitch black in an RGB Color Space and CMYK Color space.

Rich black colors also come out more vibrant and dark in print.
Conclusion:
So basically, the reason you are getting brownish black CMYK color is due to the fact you are using the wrong color space. All you need to do is fit it. Peace.
Additional Read