Blue Sector has up to 70 levels. Blue 1-3 are seen to house the command functions (C&C, Observation Dome, Medlab, station crew quarters). Because of the space taken up by the docking bay and the shuttle parking bays in the Command Sphere, it is likely that there are not so many decks here. You seem to reach Babylon 5 Customs from Blue 10: Mollari goes there to board Lord Kiro and Lady Ladira's shuttle in [SaP] which leaves from the Docking Bay, gate 12. The Customs zone is probably not situated right at the hull level, but somewhat higher, at the level of the connecting Core, with the different gates leading down into the actual parking bays. Talia Winters travels down as far as Blue 14 in [MotFL]. But the Cobra Bays appear to be reached from Blue 9 in [Sur] where Garibaldi fights the corrupt Cutter. Blue 70 must refer to the hull of the widest part of Blue Sector, which we presume is in the Torus.
This would be consistent with the earlier reference to Brown 95, the highest-numbered level of Brown Sector, mentioned in [SD]. We presume this refers to the widest part of the Carousel. The lowest-numbered level mentioned in Brown Sector (apart from the hull envelope) is Brown 2, the home of the Drazi in Babylon 5's Alien Sector in [tGoS]. Elsewhere, we hear of the level Brown 6, the home of Gera Akshi, the dancer-friend of Adira Tyree, in [BttP]. N'Grath lives on Brown 9 [SH, Sur] and the Pak'ma'ra live on Brown 8 in the Alien Sector [Leg]. Laura Rosen hides out in Brown 27 [tQoM]. The Lurkers hang out in Brown 90-95. So, Brown Sector must have a full zone devoted to it, in the widest part of the station, since more levels are mentioned than for any other sector of Babylon 5.
Red Sector is also in the widest part of the station at the opposite end of the Carousel. However, many fewer habitable levels are mentioned in the TV episodes than you might expect. The central corridor connecting all radial parts of Red Sector is on Red 5, where the Zocalo open market is found (seen in many episodes). From the low deck number, this corridor should be situated fairly close to the core, with a noticeable curvature, which is apparent in some episodes. However, the "Babylon 5 Security Manual" [SM] places Red 5 much further out towards the hull. This is more consistent with the view seen from Amanda Carter's suite 15 on Red 7 (only two floor below) [aSitW], which offers a low perspective over the open garden. On the whole, it would be preferable to site Red 5 at the higher level, and assume that Red Sector has up to 95 levels like Brown Sector. But it is possible that all the decks of Red Sector are displaced towards the hull, reserving the space at the core for additional service machinery and raw materials. Apart from Red 5, we only ever seem to visit Red 4 (a corridor in [SaP] shortly after a visit to the Casino) and Red 7.
Green Sector does not have so many levels, and provides the best evidence that floor numbering is not absolute, with respect to distance from the core. Mollari's view from Green 2 is only a moderately high perspective onto the open garden, no more than 10-20 floors above ground level. This means that level 1 starts much further out from the core than the same level in other sectors. This is borne out by views from the Core Shuttle, which shows the car high above the built-up diplomatic quarter in Green Sector, with open garden on either side. It is clear that this sector is not built very high, from the fact that views to the north and south ends of the Carousel cylinder are unobstructed for the length of the station. All of the four major alien powers have their Ambassadors residing on level Green 2. It is possible that the outer hull envelope below the garden restarts the Brown Sector numbering from level 1 again. This would make "Brown 2, level C" be the innermost pressure skin of the station (with hulls B and A further out).
Grey Sector only has 30 levels [GiM]. This is entirely consistent with Grey Sector occupying the tapering part of the station that fits inside the maglev rotation gear in the non-rotating part of the station, as described in [SM]. The wider parts of Grey Sector no doubt house heavy engineering machinery, which could occupy factories that take up several standard deck-levels. Nothing is ever stated about the deck structure of Yellow Sector. We see various views of the zero-g dock entrance; and the internal superstructure supporting the fusion reactor in the episode [Con].