Hi - unfortunately, there is no reliably consistent way to DIY lighten a colour, whilst keeping the same chroma and Hue Family location.

As you attempt to lighten it, these other attributes may alter too.

These colours are from the same Hue Family neighbourhood as Slumber Sloth, with similar chroma (degree of colour) , only lighter.

These colours are from the same Hue Family neighbourhood as Slumber Sloth, with similar chroma (degree of colour) , only lighter.

How does that help?

What should I mix with it to keep the same hue, but lighten it?

White.

You will need to experiment with the ratio to get a color you like.

It helps because Marylee is correct that you can't just add white to a color to lighten it. As she stated, whatever white you add could change other aspects of the color. There is no pure, unadulturated white, all of them have other hues in them--red, green, blue, violet, orange or yellow. There could be unintended results, like the Slumber Sloth coming out with other hues that you don't want.

Don't go down that rabbit hole. Cut your losses and use another color that gives you what you want.

Those strategic color suggestions also provide guidance, direction and most importantly a target.

Go get those paint chips.

If one of them is the right lightness, take that paint chip and all 4 gallons back to The Home Depot.

Ask if they'd be willing to try to lift the color - they might say no. Plan to be there shortly after open.

Suggest they dump all 4 into a 5, and ask if they can lift the old color towards the lightness of the new paint chip.

Odds are they'll have an easier time hitting Divine White than A la Mode.