Well for starters, a "Suriname Boa" <B>is</B> a redtailed boa. Often people label Colombian Boas aka "Common Boas" as redtailed boas but this is incorrect IMO. This was just a marketting ploy developed by dealers a few decades ago, since BCC are worth more than BCI, to make more money off the common boas. Mostly what you see labelled as redtailed boas in stores are BCI (Colombian Boas).
Now for the differences. Asides from being different subspecies, they can be quite similar. BCC tend to get larger - but some BCI can reach equally large sizes. BCC are usually more colourful as well and tend to have {} or <> shaped saddles, whereas BCI have )( shaped saddles. BCC have a saddle count of 14-22, BCI have a count of 22 or more. BCC can be a little more "sensitive" temperament wise and take more effort to acclimate to handling, but this is not always the case. BCI mature eariler than BCC do, and are generally hardier and easier to keep. Those are some of the main differences between the two subspecies, another one obviously being that BCC are more expensive than BCI. Hope this helped