The Cardano logo is presented as a dark grey or black mono logo. Although there are no official brand guidelines, the most commonly used colours are listed here. The Cardano Foundation logo uses black and a shade of blue.
Stellar’s main colour is light blue, as seen in the logo below. The not-for-profit logo heart has four secondary brand colours. The colours were sourced from the Stellar’s Press Kit.
Litecoin’s logo comprises various shades of grey, as well as Litecoin Blue for the slogan text “Smart change”. The colours were sourced from the Litecoin Style Guide.
The Bitcoin Cash logo has two colours: Bitcoin Cash Orange and Bitcoin Cash Gray. These were sourced from the PNG Logo on the Bitcoin Cash entry on Wikipedia.
The Ethereum logo contains for colours: Grey, Golden Brown, Light Grey and white. The colours were sourced from the Ethereum Visual Identity.
The Bitcoin logo comprises three colours: Bitcoin Orange (as used in the icon), Bitcoin Grey (used on the logotype text) and White.
Ripple’s logo comprises three colours: blue and teal gradient for the triskelion (symbol), and grey for the logotype. These colours have been extracted from the Ripple Style Guide.
YouTube unveiled a new logo in 2017. Their latest logo removes the “Tube” from the red button and now features the play button. The new logo also features a bolder shade of red (#FF0000), which is the strongest red in the RGB color system.
For the latest YouTube brand resources including SVG version of the new logo and play button, you should check the official YouTube Brand Guidelines.
Here are the brand colours for the Uber logo. The distinctive black and white logo is often paired with aqua.
Here are the Reddit brand and logo colours, in both HEX and RGB format.