Colours can appear darker when converting from HEX to CMYK because of the differences between the two colour spaces and the subtractive nature of CMYK. Please see the below Youtube video for more detail.

COLOUR SPACES

A “color space” is a useful conceptual tool for understanding the color capabilities of a particular device or digital file. When trying to reproduce color on another device, color spaces can show whether shadow/highlight detail and color saturation can be retained, and by how much either will be compromised.

SUBTRACTIVE COLOUR PROCESS

Here are some details about the subtractive color process:
How it works
The subtractive color process starts with white light, which reflects all colors of light. As pigments are added, they absorb certain wavelengths of light, creating color. The more color that is added, the darker the resulting color.
How it’s used
The subtractive color process is used in many mediums, including printing, painting, and silk-screening.
How to create black
In theory, combining equal amounts of cyan, magenta, and yellow will create black. However, in practice, the result is often a dark brown. To create true black, black pigment, also known as “K”, is added.
How it’s different from additive color
The subtractive color process is the opposite of the additive color process, which starts with no light and combines wavelengths to create color.
How it’s different from photography
In non-electric analog photography, the CMY model is used, but black is not used because it is not transparent enough.

LIGHT VS INK

Light and ink differ in how they create color:
Light is additive, meaning that combining colors of light creates white light. The primary colors of light are red, green, and blue.
Ink
Ink is subtractive, meaning that combining colors of ink absorbs all colors of light and appears black. The primary colors of ink are cyan, magenta, and yellow.
Here’s more information about light and ink:
Color models
There are three types of color mixing models: additive, subtractive, and average. The CMYK color model is used in printing, silk-screening, and painting. In CMYK, black is added to produce deeper black tones and to save on ink.
Highlighter ink contains chemicals that absorb visible and ultraviolet light.
Color perception.
The RYB primary colors were the basis for 18th-century color vision theories.

BRIGHTNESS

Here are some tips for making CMYK colors brighter:
Use high intensity
The intensity of CMYK colors ranges from 0 to 100, with 100 being the highest intensity. For example, to create pure cyan, the CMYK code would be C100, M0, Y0, K0.
Use high magenta levels
For stand-out pinks, use high magenta levels and low yellow, cyan, and black levels.
Use the curves setting
In the adjustments menu, choose curves and set the top button to gamma to strengthen all the channels equally.
CMYK is the primary color model for printing, while RGB is the primary color model for displaying on a computer screen

COLOUR CONVERSION - CMYK, HSL, HEX AND RGB

https://convertacolor.com/

Port Macquarie

CMYK EXPLAINED