Sexual ornaments need to be conspicuous to be effective and there are multiple ways to achieve this. Two main ways are 1) by increasing the ornament's colour or brightness contrast against the background and 2) by increasing the size of the ornament. Conspicuous ornaments also carry a greater risk of predation. We assess the relationship between the colour and size of the dewlap of several species of gliding lizards (genus Draco) from Malaysia and the Philippines. We found a negative relationship between colour contrast against the background and relative dewlap size, suggesting that increasing colour contrast and relative dewlap size are alternative strategies for effective communication. Male relative dewlap size increases with increasing sexual size dimorphism, and dewlap colour and brightness contrast increase with increasing sexual dichromatism in colour and brightness respectively, suggesting that sexual selection is acting on both dewlap size and colour. We further show that species employing greater relative dewlap size for conspicuousness are those found in high predation habitats, whilst species employing greater colour contrast are found in relatively low predation habitats. These results suggest that the use of larger or more colourful dewlaps as strategies for effective communication may be driven by the interaction between sexual selection and predation risk.