  Virtual observatories allow the means by which an astronomer is able to
discover, access, and process data seamlessly, regardless of its physical
location. However, steep learning curves are often required to become
proficient in the software employed to access, analyse and visualise this trove
of data. It would be desirable, for both research and educational purposes, to
have applications which allow users to visualise data at the click of a button.
Therefore, we have developed a standalone application (written in Python) for
plotting photometric Colour Magnitude Diagrams (CMDs) - one of the most widely
used tools for studying and teaching about astronomical populations. The CMD
Plot Tool application functions "out of the box" without the need for the user
to install code interpreters, additional libraries and modules, or to modify
system paths; and it is available on multiple platforms. Interacting via a
graphical user interface (GUI), users can quickly and easily generate high
quality plots, annotated and labelled as desired, from various data sources.
This paper describes how CMD Plot Tool was developed using Object Orientated
Programming and a formal software design lifecycle (SDLC). We highlight the
need for the astronomical software development culture to identify appropriate
programming paradigms and SDLCs. We outline the functionality and uses of CMD
Plot Tool, with examples of star cluster photometry. All results plots were
created using CMD Plot Tool on data readily available from various online
virtual observatories, or acquired from observations and reduced with
IRAF/PyRAF.
