Keynote offers flexibility in the type of graphics you can add to your slide show presentation. A nice graphical touch is to layer transparent blocks of colour on the slide by using the opacity level in Keynote's Graphic Inspector. Transparency adds depth and softens images, allows for text to be legible behind a block of colour and adds interesting effects to the other images on your slide.
Open Keynote by clicking on the program's icon in your dock. The Keynote icon resembles a wooden podium. Highlight a theme style for your presentation by clicking on it, then click "Choose."
Click the slide on which you want to add transparent colours. Click the "Shapes" tool in the toolbar. Select a shape from the pull-down menu. Note that the shape has handles surrounding it, which means it is selected on the slide.
Click the blue "Inspector" icon in the toolbar, then click the "Graphic Inspector" icon in the centre of the Inspector tool bar. This icon resembles a small green circle in front of a square.
Click the text box below "Fill." Select "Color Fill" from the pull-down menu. Make sure your shape is still selected. Click the colour sample square to choose a fill colour from the colour palette. Place the magnifying glass on your preferred colour in the colour palette and click to select it. Your shape is now filled with a solid colour.
Drag the slider at the bottom of the "Graphic Inspector" to change the opacity of the colour fill. Decrease the opacity to make the colour block transparent by dragging the slider to the left. Alternatively, enter a transparency percentage value in the box to the right of the slider.