Visual perception can be affected by training mental representations. However, it remains unclear if training procedures can also affect the quality of mental representations. To investigate if training enhances the fidelity of mental representations retrieved from visual long-term memory (VLTM), we used a task including object-color associations with a continuous response-space. We tested 15 participants in a training group and 15 participants in a control group. Training consisted of six training runs executed on 3 consecutive days. Before and after training, we assessed accessibility and fidelity of mental representations in VLTM and of single objects in visual short-term memory (VSTM). Not only accessibility to mental representation but also their fidelity increased across training and transferred to novel object-color associations in VLTM and VSTM after training. At the end of the training, fidelity of VLTM representations were virtually identical to fidelity of VSTM representations. We conclude that training object-color associations does not only improve the accessibility of VLTM representations, but also their fidelity based on perceptual plasticity of the visual system.