Usually this red paint is used to point out the Re-entry vehicle carried by the Hatf-I (BRBM), Abdali-I (BRBM), Ghauri-I (MRBM), Ghauri-II (MRBM), Shaheen-I (MRBM), Shaheen-II (IRBM) and in case of Babur (Cruise Missile) Hatf-VII, Ra'ad (Air Launched Cruise Missile) Hatf-VIII to represent the warhead section of missile. T
his may or may not be the case once missile is in operational service for example there are several pictures of Hatf-III (Ghaznavi) Ballistic Missile System and Babur Cruise Missile Hatf-VII without this red paint.
Now comes the black paint the end of Re-entry vehicle carried by the Shaheen-I (MRBM), Shaheen-II (IRBM). Both Shaheen-I (MRBM), Shaheen-II (IRBM) Re-entry vehicle carries radar correlation terminal seeker to achieve extremely accurate CEP in range of 20-50m or even less
Re-entry vehicle carried by the Shaheen-I missile have a mass of 850kg.Shaheen-II missile have a mass of 1050kg. This re-entry vehicle mass of 1050kg carry Nuclear Warhead weight of the re-entry vehicles itself and a
terminal guidance (as confirmed by Dr. Samar Mubarakmand)which is most probably radar correlation terminal seeker to achieve extremely accurate CEP in range of 20-50m similar to US PERSHING II. Shaheen-I missile ‘s re-entry vehicle have four moving delta control fins while re-entry vehicle of Shaheen-II missile unlike that of Shaheen-I does not have four moving delta control fins at the rear and small solid/liquid-propellant side thrust motors. Both moving delta control fins and small solid/liquid-propellant side thrust motors are used to orientate the re-entry vehicle after boost burn out or before reentry to improve the accuracy by providing stabilization during the terminal phase.
These are also be used to fly evasive maneuvers, making it immensely problematic to intercept by any existing anti-ballistic missile defence systems. As Shaheen-II may change its trajectory several times during re-entry and even during the terminal phase,
effectively preventing pre-calculated intercept points of radar systems - which is a method nearly all ABM systems using these days. This re-entry vehicle also has GPS updates to further improve its CEP.
I hope this would have cleared few of your questions