Change colours in PowerPoint all at once

If the deck uses theme colours

When shapes and text are coloured with the theme's colours, PowerPoint can change them everywhere in one go.

1. Open the Design tab and find Variants.
2. Open its menu and choose Colors, then Customize Colors.
3. Set the new accent colours and save. Everything that used the theme colours updates.

Many decks use fixed colours instead, picked from the colour wheel or copied from another file. Those do not move when the theme changes, which is why this often seems to do nothing.

If the colours are fixed

1. Open the Selection Pane (Home > Arrange or Select > Selection Pane) to find hidden or grouped shapes.
2. Select every shape that should change, holding Shift, then use Shape Fill, Shape Outline and Font Color.
3. Repeat for each colour and each slide, and check that text is still readable on the new backgrounds.

It works, but on a long deck it takes hours, and text on a dark new fill is easy to miss.

Recolour in one click with KPT Style Basic (free)

KPT Style is a free add-in for PowerPoint for Mac and PowerPoint for Windows (beta). It adds a tab to the ribbon.

1. Select the objects you want to change, on one slide or several.
2. Pick one of the ten palettes, or the deck's own theme colours.
3. Press Recolour. Fills, text and lines change together, and a contrast guard keeps text readable on its new background, to the WCAG AA standard.
4. Changed your mind? Reset puts back the original colours for the selection or the slide.

The same tab has Scale by %, which resizes a selection together with its text and line weights, with a preview.