Clicking on the little arrow on the right of a layer in the Layers palette opens a drop-down list where you can pick a colour from red, green and blue to apply to the layer. Once colours have been applied a new merge layer can be made by selecting the layers you want to merge and dragging them to the New button at the top of the palette or selecting 'Merge to RGB' from the Layers menu. A bright-field image can be merged with fluorescence by placing it above the fluorescence layer in the palette, changing its opacity and then selecting 'Merge to Composite' from the Layers menu. Colours other than RGB can be applied using the colour swatch in the document window tool bar. | 