You can divide this into two astronomical epochs, which are most easily understood in terms of the Hertzsprung-Russell diagram.
The first is the pre-main-sequence (PMS) phase, where the protosun contracts towards its main sequence, hydrogen burning, configuration. During this phase the (proto-)Sun declines in luminosity at roughly constant temperature for several million years, then heats up, with a slightly rising luminosity, before settling onto the main sequence with a slightly lower luminosity (see diagram below) after about 20 million years. The diagram gives you a rough idea of the "colour" that the protosun would have during this phase. The Sun is of course changing in brightness accordingly, but the radius of the Sun also decreases throughout this phase, so would cover a progressively smaller angle on the sky as seen from the Earth.
$$ R = \left(\frac{L}{4\pi \sigma T^4}\right)^{1/2}$$

A plot showing the paths (solid lines) of stars of different masses from birth (the Sun is still $\simeq 1M_{\odot}$ at birth) in luminosity and temperature, until they begin the H-burning main sequence. The dashed lines are "isochrones" at the indicated ages. The Sun "begins" its life (or at least emerges from its natal gas and dust less than a million years after birth) at the top of the $1M_{\odot}$ track.
The second phase is of course much longer, but the changes are far less dramatic. For the next 4.45 billion years the Sun just gets a little brighter and a little larger, but stays more-or-less at the same temperature. Over that time the Sun has got about 30% more luminous and 15% larger at a roughly constant rate.
If you need more detail than that, then you need to access a proper stellar evolutionary model. There are lots of those available. e.g. the Geneva models (the Schaller et al. 1992 set are appropriate for the Sun).